Where can I find an SKS receiver cover?

I bought a spare SKS off townpost. I wanted just a fuck around gun while keep my original (first gun I've ever bought) SKS as a safe queen.

I picked one up with an ATI stock, it was in rough shape, but cleaned her up, and she's shooting. Issue is, it also came with a pic rail receiver cover. Which just moves every time I shoot it. No point in keeping a scope mounted, it won't hold anything remotely close to zero.

I can peep through the rail for irons, but its not as comfortable.

Is there any place that just sells parts?

I don't want to buy a whole donor rifle, and I can just live with it. But spare parts never hurt.