Your Yugo SKS can use any NATO 22mm Rifle Grenade. Any 22mm Rifle Grenade will work. The key is YOU MUST USE A RIFLE GRENADE BLANK. If you use a live round. Your gun will blow up.
Below if a photo of the Israeli 22mm Training Kits that were sold a while ago.
Also the US made M1A2 Rifle Grenade will work.
Here is a place that has some in stock. CLICK HERE
Lots of folks get these and use them with tennis balls.