Yes. If you're already pledging at a level that has a T-shirt award, please just add $15 per extra shirt you want, and let us know that was your intent when you send us your shipping details, etc after project funding.
We don't have a preview of the comic version ready yet, but you can read the first two chapters of the novel by downloading our free preview (http://bentobooks.wpengine.com/wp-content/uploads/2011/10/Math-Girls-Sample.pdf).
While the pledge descriptions say that your pledge covers shipping to addresses in the continental US, we've subsequently looked more closely at shipping rates to other US addresses, and it turns out that rates aren't all that different. If live at a non-48 state US address and you'd like to add an extra dollar or two to help us cover that you're certainly welcome to, but we'll still ship to you at the regular pledge levels.
Don't see the answer to your question? Ask the project creator directly.