Hi
If you have pics, we can better understand the issue. If this bit is very worn other areas are likely to be very worn too.
Chambers don't list a piston but John Knibbs (or Mark) may be able to help.
However, if it really is only wear in the sear engagement region I'm sure that it could be repaired effectively but a competent gunsmith/welder/model engineer as a much cheaper option
Best of luck
David.