Jessops still has them but that availability varies very very widely. Might be easier if you ask someone if they see any to go pick them up. I can't remember if those were 100 or 400, either. I think they were 400 but you might be able to get 100.

Silverprint seem to have a make your own kind of kit for making whatever speed DX coding you need.
http://www.silverprint.co.uk/acc17.html