I think the reason we don't see them is that they fell out of use upon the advent of the square rule in the first quarter of the 19th century and being a fairly non-descript tool, were reforged or abused into obscurity. (that's just my theory though)
we had ours made out of stainless steel by a machine shop. They turned turned a taper we specified and then welded a t-handle on them.
They are incredibly useful tools, especially during raisings, to temporarily pin a joint securely. I am surprised you don't see more in the states -- pretty much every shop in the UK uses them (but they are scribing).
To answer your question, I don't know of any source of framing pins other than having them custom made. Ours cost around 30 bucks each. I am sure you could get some cheaper ones if you didn't want the T handle and didn't uses stainless. But I wouldn't change a thing about ours.
gabel
