There are specific ones for the 500. I do not see the 535's listed on any websites yet, I think it might be because of the newness of the gun. the 535 ATS is new for 2005 so I'm not sure if you can get scope mounts for it.
You might get lucky and they fit though.
If not perhaps you know someone that can machine you new holes, the only problem is if the screw threads are different you will mess up the threads, unless you can get someone to re-tap the holes for you too.
I trust midwayusa to have something if it's available, either them or www.cheaperthandirt.com