I?m actually thinking of going 3 lug on all my guns. My QD suppressor is easier than direct thread. But direct thread is cheaper. No lugs and QD.
As for a threaded 3 lug, you may be able to order one from Zenith Firearms. My Z5P came with a threaded 3 lug that I am actually thinking of installing on my Scorpion for the purpose of using my flash can when not shooting suppressed.