Yep just buy mags for what you got. I'd buy mags before modifying a receiver to take a different mag, any day of the week. I faced that debate with my first AK, a $250 new Saiga that only took proprietary 10 round mags. The aftermarket fixed that, but that special made 30 round mag was priced at $50 a piece when regular steel commie AK mags were selling like new for only $10, buy 5 or 6 and get the surplus pouch for free. So I learned my lesson and sold that Saiga rifle. No way was I buying $500 in 10 mags when I could pay $500 and get 50 regular AK mags
You should have converted it - few minutes in the shop installing a bullet guide and you could have run those cheap steels. Bummer, that's a $1.8k (ish) rifle now.