Where can I get a replacement Reflex Mirror for a vintage SLR Camera?

I bought an old Nikon FG SLR camera at a local thrift store for $6.40. The body is great, the lens is still in good condition, problem is, it's missing the reflex mirror inside the camera. I know that's a crucial part of the camera and I was wondering if you can get a replacement for it. If so, where can I get one? I tried looking on Ebay and I can't seem to find any.

You can buy an entire FG body in nice condition on eBay for under $30, so is it really worth it to try to replace the mirror? If it is anywhere near as complicated as my Nikkormat FTN, you will not be able to install the mirror without breaking something else, and it is likely that you wouldn't even be able to install the new mirror and have it function correctly. In my opinion, it would be much easier to just buy another body that is fully functional, and keep yours for parts (if you ever need them).

You may try your luck here. They might be able to find the reflex mirror for you. Go and ask for it.