I normally get my shirt from product launches that I go to.
Plus I got my HP Rep that comes around, how ever they always seem to give me shirts that are one or 2 sizes too small.
I have 2x HP Polo shirt and 2x Mitsubishi Business shirt. You want them. Come get them.
Contact the manufactures. They will either send you some, or point you in the direction of purchasing some.
Personally I am aganst the idea of paying money for these things as I am really being a free advertisement board.
ALTHOUGH, I do have my FULL AMD ATHLON FX Shirt, Jacket and Hat that I wear at every Intel GID Meeting.