If you own a C64, you could test the SID with the computer, otherwise I see no chance without a PIC.
However, when I look into my shelf which is full of electronical components I see a lot of PIC16F877-04 which I got as samples from a german distributor. He sent me the 4 MHz version by fault but never wanted them back. I used two of them some weeks for my SID modules (overclocked!), but now I’ve replaced them by PIC18F452. Since I’ve no use for these PIC16F chips anymore, I could give you one for free, just email your postal address
In the meantime you should try to find the root cause for this failure, so that it never happens again!
oh - I overclocked the chips with 20 MHz and noticed no failures (I had luck!). But ok, so I have to search for another useful job for the chips. Maybe I should build even more SID units