Here is are some other stores that sell x0xb0x kits or 303 clone related things.

x0xsh0p.de Has kits, parts and a cool VCO mod. 

openmusiclabs.com Sells the x0x-heart and pacemaker PCB for a x0xb0x in your eurorack. Also a good resource for easy to read x0xb0x schematics.

rv0.be Get your x0xlarge CPU upgrade here. Also has panels and a few other parts.

abstraktinstruments.com If you need a non DIY analog 303 solution the the avalon bassline is the way to go.

shop.re-303.com  DinSync is working on getting a exact replica of a TB-303. The ultimate 303 clone