This might help

https://www.gatewaytoairguns.com/airguns/index.php?topic=13034.0

My understanding is that the Slavia guns were common in Canada and Europe. You may find parts there.
Chambers in the UK is a good starting point, and you may want to post your request on one or two Canadian forums, plus Gateway to Airguns.

If I find a diagram or any other goodies, I'll post a link here as well.

Good luck with the rebuild!

Work is what you do to finance your real life.....