15. Question is where to get the parts from? Well, don’t worry, I did the leg work for you…

Go to Mouser Electronics (I don’t work for them), I included a link below to their website, and order as many as you’d like. A Roland BK-9 needs 10 linear pots, I would order some extra ones, in case you'll need them in the future.

https://www.mouser.com/ProductDetail/Alps-Alpine/RS301111A01G?qs=6EGMNY9ZYDQJz7Y655fPIQ%3D%3D