Green Mountain Monogram is the company that did the Power Tour shirts. http://www.greenmtmonogram.com/
I didn't see a place to buy shirts on there though.
I would try giving them a call at the number on their site: 800-639-2033
2001 SOM SS M6 - Longtubes, GMMG, SLP MAF, Lid, CAI, 3.73s, a little carbon fiber here and there, cross-drilled rotors, Fikse FM-5s, Koni SA, Hotchkis springs, etc... 350 RWHP, 360 RWTQ - garage Queen
1970 Chevelle SS454 Fathom Blue/White Stripes - garage KING
2002 Tahoe LS - Navy blue
2013 Cruze LT RS - blue topaz metallic, daily driver