Which Konus RDS do you have? Most, but not all of them come with riser mounts/blocks. Did yours not?
Midway has two pages of picatinny risers. You’ll simply need to know the height and length you need. I typically don’t give much thought to the risers I use - as long as they are true and tight, it’s basically just a brick, so paying top dollar often doesn’t buy anything which isn’t bought with a lower cost option. I know I have a cheap UTG riser under one red dot - the finish sucks and the big thumb screw is janky, but guess what - it holds just fine. I also have Weaver, Wheeler, Burris, Bushmaster, Badger, and I’m sure a couple others I’m forgetting, and they all work.