Here's a source -
This is for the more common .22LR version of the SA-22. The same source has one for .22 Short. Check the marking on your barrel before ordering.
If there is nothing else missing, replacing this part should fix it. I believe this is "drop-in" (no fitting necessary).
However, it wouldn't be a bad idea to have a gunsmith look the rifle over if its history is at all questionable.