Is this part of the trigger you're talking about, or part of the switching unit? I've owned an AK for 7 years and I'm not sure what you're talking about, but it sounds like the upper part of the switching unit. Switching units are easy to find both Systema and Guarder make ones that I've had good success with. I've not used the CA stuff, but it's available locally from Xtreme Tactics or ASCA in the retailer bar. I've never seen the switching components available individually, though; only as a set.
http://www.uncompany.com/pageproduct...sp?prodid=8708
http://www.uncompany.com/pageproduct...sp?prodid=9381
(
www.airsoftparts.ca does UNCo orders every month)
http://www.ascarmoury.com/product_in...roducts_id=629
http://xtreme-tactics.com/store/prod...roducts_id=233