Fine. Buy 100 shirts and set up a booth at the game. Sign up, get a shirt - its a loss leader at that point.
But I'm telling you, having been directly involved with the CAF, it's not going to happen. First, its a slipperly slope, like I said. You give shirts, now people complain that they aren't cool enough, or like I said its not cut for a woman, or they want gray not red - bitch bitch bitch. And when you have big donors bitching about little things like a t shirt, you have to do something, so yeah its one more thing.
Also, lets make a business case for the t-shirts - There are what, 6000 CAF members? Lets say you get a smoking deal on some shirts and they cost $2 each, so you're in $12k. To break even, you divide average gift into that number - last I saw it was in the low $100's, so lets say $125. That's 96 new CAF members - at the average donation level - just to break even. Don't forget, for this to be a solid business case that growth has to be above what you are already projecting, due to additional costs.
Is that scenario possible? Its possible, but is it probable? Tough to say, but if I were making a decision on whether or not to commit time and resources to this as a revenue generator, I wouldn't.
If you want to make a case to do it as good will, that is another discussion altogether.