Any question answered...

Any decent fastener shop

UNC here
http://www.imperialnutsandbolts.com/fasteners-and-fittings/low-head-socket-cap-screws-12-9-self-colour/unc-low-head-socket-cap-screws-12-9-self-colour/low-head-socket-cap-screw-grade-12-9-self-coloured-3/8-unc-sets/prod_686.html

UNF here
http://www.imperialnutsandbolts.com/fasteners-and-fittings/socket-head-cap-screws-12-9-self-colour/unf-socket-head-cap-screws-12-9-self-colour/socket-head-cap-screw-grade-12-9-self-coloured-3/8-unf-sets/prod_597.html

Can't remember which thread pitch you need, I think it's fine.

It's 24tpi, unfortunately those look like their head is too small so will just screw into the axle without securing the cranks.