Look for window sash guide part replacement

Hi - 
 
I'm looking for a specific window sash guide part. I recently bought a new house, and it looks like the windows were installed sometime in the 1980s. I'm hoping you might carry this part, or at least be able to help me identify it. If you don't have it in stock, I’d really appreciate any guidance on where I might be able to find it. Also, if I purchase the part and it ends up not fitting, would I be able to return it for a refund? Thank you!