Claire,
I have purchased solid brass "Clinching nails" for use in shoemaking. You need to use an anvil with them as they have a side point and are designed to strike the anvil and curve back up to the head of the tack. I purchased them from Zackwhite.com. They also sell brass "lace tacks". http://www.zackwhite.com/2532-12-Solid-Brass-Lace-Tacks-1oz-Pack--TT95912_p_3655.html
I'm not quite sure what they are for, but seem to have a square shaft and may be useful to you. I don't know about UK suppliers, sorry.
Regards,
Betsy
