You can get a MK II STEN kit from Apex gun parts, Numrich, Desert Fox, Atlantic Firearms,or Sarco inc. Some Kits come with barrels, some not. Expect to pay around $170 for one without a barrel and having a T stock, to $260 for one with 16" barrel and a skeleton stock. I bought a kit without barrel and then paid $54 for an 8 inch barrel and welded an extension to it...it's hidden by the suppressor. Then you have to buy a tube, and semi-auto parts kit for around $260...I recommend
https://www.indianapolisordnance.com. You want to build a MK2 STEN...it has the most readily available parts. Then you have to buy some mags...anywhere from $10 to $20. Plus, for the suppressor, you'll have to buy a barrel nut and have it threaded...$35 for the nut. So it's not cheap, everyone is drawn by the $161 "parts kit" but there is a little more to it, with a lot of machining and welding. Not for a beginner. On the other hand, it appears semi-auto STEN's sell for around $1400.