Not sure where to post this but since there are many AK kits with depleted tritium sights I figured I'd put it here.
I found some at the "Candlepower" forums in the FS section. They are shipped as replacement vials for a tritium-powered keychain FOB.
Not a bad price, either!
The keychain fobs called "glowrings" have larger inserts:
If you search for "tritium" on that FS forum you can probably find some more. It would take a very small amount of work to get these into the Yugo rifles for replacements, or to convert the painted-on night sights to these with a small drill, some silicone RTV caulk and patience.