MK5 Golf GTI

Guys, I'm desperate, I tried to rebuild my Golf V 2004 1.9 TDI Rear brake caliper this weekend and somehow I managed to break a snap ring which is inside the caliper (not in the piston) And now I can't find the replacement part, can't even find the part number. I would really appreciate your help in finding the part number. The photo of the ring is down bellow. Caliper is TRW with a 38 mm piston.