If you want to use the power-T, just email somebody in the athletic department office to direct you to the right person. Ask them for permission. Tell them it's an original design, not for profit. It's just for people on Volnation who want it, and you're going to donate some of the proceeds to charity. Make it a donation to the athletic department, or the scholarship fund or something, to sweeten the deal.
Or, just make the damn shirts! If you're not doing it for profit, they won't be able to do anything about it, nor would they want to, because they would be alienating fans. I've seen the same thing come up with enthusiasts' car clubs making calendars. It's either about profit, or about how the trademark is used. If you're not doing it for profit, and you're not using it in a way that puts the university in a bad light, then you'll be OK.
Another thing you can do is make a minor change to the symbol. For example, use a similar, but not identical font. Then it isn't technically the power-T. Legally, it's just a T, even though everyody looking at it knows what it's supposed to mean. They don't have a copyright or registered trademark on the letter T, you know. I'm pretty sure every letter in the alphabet is public domain. I've seen plenty of non-licensed products with what looks like the power-T on them, but it isn't an exact image. I drive a Lotus, and whenever I'm interested in buying something with the Lotus logo on it, like off of ebay, I have to look closely. A lot of them have left off just a small part of the actual logo (like the tip at the top of the letter "C" in the initials) that you have to look closely to notice. It gets them around the trademark and copyright laws.
