Off the top of my head
Type 56-1
1. Any RIS designed for a real AK-47 front end will work.
CYMA AKS-74u
1. Use a rail adapter on the side optic rails, but you lose the ability to fold the stock.
2. Front RIS
http://www.ebairsoft.com/aabb-alumin...4u-p-6178.html
There are a few others, like Rails that replace the rear sight and rails that co exist with the AKS-74u rear sight, but they aren't built for airsoft gun dimensions.
Hope this helps