i picked up some stick magazines from sportsmans guide for $20 i think.just had to open up the hole in the back of the mag so they could lock up.never had any issues with them.
I owned the Pistol model A-5. When the drum is emptied, You have to hold the bolt back in one hand, depress the mag release with the second hand and then with your third hand slide the drum out. ( Mine was tight ). All this and a gun that jams makes a day at the range unsatisfying. "Generic" Thompsons look great but majority of them fail to cycle. Use the stick mags for ease of shooting and the drum for looks. I sold mine!
even though it's not milsurp, does that still fire from the open bolt? and isn't the thompson blowback operated? i'm just curious how those two characteristics affect accuracy, but i guess that's just the dork in me. i realize you don't buy a thompson for competitive shooting. i can't afford a thompson, but if i could i'd have one...so cool.