Well you could try Numrich gun parts online or contact them. They have parts for all kinds of stuff, maybe Jennings too. They have parts for some lines of economical (let's say) guns going way back, but it might be hit or miss, the parts may be used but serviceable. You might have to give a request and as much info as possible and they will check their parts bins. Their inventory has not been too organised or computerised in the past on odd parts, therefore some patience might be called for while they check for it. If you have an exploded view of the gun that is helpful too.
Your gun is like your nose, it is just wrong for someone else to pick it for you!