It was way back in early May that the kernel source for Sprint and US Cellular Galaxy S4 variants showed up on Samsung's servers. The Virgin Mobile Canada edition was added in April. The Verizon and AT&T devices came in the following weeks, but no peep from the T-Mobile version. Well, until today – Samsung just posted the T-Mobile GS4 kernel source in all its glory.
As usual, the Jelly Bean source is available on Samsung's site for any developer-type or curious onlooker to grab. Now that the Tmo source is up, that pretty much takes care of all the carrier-branded Galaxy S4 devices. Enjoy.