Hi, I would recommend taking a look at Primary Weapon Systems. They have a long stroke piston system like the AK. They also have a 3 position adjustable gas block which helps a ton if you shoot suppressed. Plus their warranty and customer service were great the one time I had to contact them. I broke the operating rod cause I didn't know what I was doing and they replaced it for free.
Some other piston operated AR's to look at would be LWRC, LMT and, the Sig Spear LT. Sig actually has made a few piston AR's but I can't keep track of all their model numbers. Theres also Type A, Adam's Arms and Caracal. Im sure there's more that im not mentioning. Figure out what features mean the most to and narrow it down from there. Good luck!