The R & D conversion cylinders do not have firing pin return springs. They are intended by design to "float" in the breach plate. There actually isn't room in the breach plate for springs under the firing pins. If the firing pins are "sticking" you may want to check the back of the firing pin to see if they are starting to "mushroom" which will cause sticking. The firing pin, if mushrooming will have to be dressed down or replaced.
Trigger bolt springs can be had as posted above. I don't particularly like wire trigger bolt springs. An alternative for a lighter trigger bolt spring is a Pietta trigger bolt spring. Available from VTI Gunparts.
Coffinmaker