My dutifuller half,
waxjism, who is off to assemble greenhouses for her mother in the rain today, finished this rather small laceweight shawl for me which we haven't blocked yet because we don't have blocking wires; but she astutely asked "Can we make our own?" this morning.
So I googled it, and it turns out that the blocking wires sold as such tend to be stainless steel wire or rod in lengths somewhere around a meter or a bit less and varying from just under 1 mm to around 1½ mm in gauge. This is sold for welders to fill in gaps with, apparently just via welding supply places in North America because North American hardware stores don't necessarily stock it, but our building supply and hardware supply ecosystem is a bit different and Wax was able to pick up two rolls today.
(Side note: it's far from surprising that this knitting accessory is a huge ripoff. There's a proud tradition of selling things like foam puzzle floor mats to knitters with a little rebranding at something like a 300-400% markup, to say nothing of the A5 zipper binder full of pencil pockets I just saw being sold as a circular needle organizer for sixty bucks. Are you kidding me?????? Get an A5 binder or a CD wallet! Honestly! A markup like that, and it's made of PU and isn't even attractive! At least expensive stitch markers are typically priced because of the labor involved in somebody else using jewelry-making supplies to string the beads and things onto the loops!)
I'm still going to order a bunch more pins, which we definitely need - I run out even blocking sweaters sometimes - and my googling also informed me that people substitute undyed, untreated yarn (eg kitchen twine, basic crocheting or macrame thread), unwaxed dental floss, or even some kind of plastic thread for the wires as well, particularly over curves and longer stretches. The difference is that string, of course, has to be pulled taut on the straight sides, which requires wrapping the ends around pins and so on.
Unless your edge isn't straight, that is, as you can see from this image from Scottish designer Kate Davies' hap stretcher tutorial:

(washing and dressing Shetland haps in the early 1900s) via Kate Davies Designs
We have the spare stretcher frame for a large canvas because we ordered the wrong size for our Karkuteillä the first time around, but it doesn't have any pegs or anything like that, so our tentative idea is to stretch an old sheet over it and pin to that.

"Karkuteillä" ("Runaways") by Maija Louekari for Marimekko
With giant things like blankets, people often use mattresses or wall-to-wall carpeting, only one of which we have. However, the Yggdrasil blanket Wax is nearing the end of might even be too large to stretch over our mattress when it's finished, and in that case I guess we won't have any way to stretch it at all unless we want to attach hooks to the furniture and stretch it out through the air in the middle of the room. Perhaps simply finger-blocking will suffice. It's not a lace shawl, after all.
So I googled it, and it turns out that the blocking wires sold as such tend to be stainless steel wire or rod in lengths somewhere around a meter or a bit less and varying from just under 1 mm to around 1½ mm in gauge. This is sold for welders to fill in gaps with, apparently just via welding supply places in North America because North American hardware stores don't necessarily stock it, but our building supply and hardware supply ecosystem is a bit different and Wax was able to pick up two rolls today.
(Side note: it's far from surprising that this knitting accessory is a huge ripoff. There's a proud tradition of selling things like foam puzzle floor mats to knitters with a little rebranding at something like a 300-400% markup, to say nothing of the A5 zipper binder full of pencil pockets I just saw being sold as a circular needle organizer for sixty bucks. Are you kidding me?????? Get an A5 binder or a CD wallet! Honestly! A markup like that, and it's made of PU and isn't even attractive! At least expensive stitch markers are typically priced because of the labor involved in somebody else using jewelry-making supplies to string the beads and things onto the loops!)
I'm still going to order a bunch more pins, which we definitely need - I run out even blocking sweaters sometimes - and my googling also informed me that people substitute undyed, untreated yarn (eg kitchen twine, basic crocheting or macrame thread), unwaxed dental floss, or even some kind of plastic thread for the wires as well, particularly over curves and longer stretches. The difference is that string, of course, has to be pulled taut on the straight sides, which requires wrapping the ends around pins and so on.
Unless your edge isn't straight, that is, as you can see from this image from Scottish designer Kate Davies' hap stretcher tutorial:

(washing and dressing Shetland haps in the early 1900s) via Kate Davies Designs
We have the spare stretcher frame for a large canvas because we ordered the wrong size for our Karkuteillä the first time around, but it doesn't have any pegs or anything like that, so our tentative idea is to stretch an old sheet over it and pin to that.

"Karkuteillä" ("Runaways") by Maija Louekari for Marimekko
With giant things like blankets, people often use mattresses or wall-to-wall carpeting, only one of which we have. However, the Yggdrasil blanket Wax is nearing the end of might even be too large to stretch over our mattress when it's finished, and in that case I guess we won't have any way to stretch it at all unless we want to attach hooks to the furniture and stretch it out through the air in the middle of the room. Perhaps simply finger-blocking will suffice. It's not a lace shawl, after all.