We are working on something like that, believe it or not!
First we'd like to encourage people to attend the closest screening. If that won't work, then order the shirt from a Browncoat group online who is willing to ship (so long as the person pays for the shipping) to those who cannot attend. After all those options are retired, then we are working on having something set up so people can buy anytime. It's a matter of who, how, where and when and we're working on it.
Our biggest concern is that the local organizers/screenings are able to receive as many sales as they can before we "open the store" so to speak. That's our priority.
We also have a couple other shiny secrets which would benefit from this. Cafe Press is cool but it does get a bit expensive. But we shall see what we can do. And yes, we'd love to hear all of your thoughts on this.