Alternative ESB Scope

For ESB - the scope is the AST 4x20 - I think. Are there any close alternatives? Thanks guys.

Check ebay and just make sure it's the right length. I got mine from Asia Hobby Airsoft for 10 dollars shipped. It's fully functional too which is cool...

The only thing that is a major noticable difference are the mounting brackets...

I think it needs to be close to 11 inches in length. I almost bought one that was a much shorter length by mistake.