Parts and part numbers:
.40 FSR Ring:
.40 FSR ABC
Piston/liner assembly: 24903002
These are all discontinued parts, You may be able to locate parts through someone who deals in old engines and sells to the collectors' market. Some of these people advertise in the classified section of the model magazines. An internet search may yield some results. Posting a "parts wanted" ad in the RCU Marketplace may help.