These BB OS isn't sold to users
You can get em from the BB site for free... but locating them may be a task
Luckily for us, the Mods and other great members here give us the links where we can find the latest (and older OS)...
But I've check some T-Mo links and can't find the OS you're lookin for.
You'll have to do some searching for it:
How do I downgrade the OS on my BlackBerry?
There's another link in the instructions where you can try searching for the OS you want.
Good Luck!