If you are Stateside (USA) theres a place called Empire Airsoft, they are the only spot I've found direct replacements for the TW5 Lug. They have a standard metal version and a threaded version with -14mm threads.
http://www.empireairsoft.com/advanced_s ... ds=tw5+lugAnother option (what I did) is to get a MP5K adapter and drill the inside out some to fit over the inner barrel diameter. I don't remember what size drill bit I used, but I matched the bit with the orange flash hider inner diameter, then clamped the adapter down and drilled it out. It slid over the barrel and threaded right on, now I can use any flash hider, suppressor, or tracer I want with -14mm threads. This has been done by a few others I have seen, so I am not taking any credit for the adapter as I've got the idea from someone else.
http://www.redwolfairsoft.com/redwolf/a ... thread.htmhttp://www.redwolfairsoft.com/redwolf/a ... thread.htm