Is it possible to replace the seat rails on a saddle? My saddle's rails have become bent so that the saddle is askew. Rather than get a new saddle, is there any way to replace just the rails?

I assume bending them back is useless, as even if i could get them totally straight they would be weakened and just bend again.
High end saddles like Brooks do offer rail and frame replacements: http://www.brooksengland.com/en_us/spare-parts.html

You might google "yoursaddlecompany rail replacement"

But if your saddle cost less than US$50,
I doubt it is economic to do so. Stocking SKUs and supporting a repair/parts department costs money for the saddle company. 

You're better off either just getting a new saddle or seeing if you can't buy a used saddle with a trashed seat cover and doing a transplant. Note that many saddles are riveted on so this may be a big pain.