I've been looking around myself for buying some seeds to grow a few plants in my closet. A lot of sites DON'T ship to the U.S. but I've found a few (I'm also in the U.S., Mass.). I e-mailed this site a few times and have spoken with them about shipping to the U.S. and they say they ship everywhere worldwide it's up to you not to get caught with them.

Site:
http://www.amsterdammarijuanaseeds.com/

I don't know how reliable they are though but read this:

"We ship all marijuana seeds in crush proof CD-ROM sealed envelops with no indication to the contents."

^ That's pretty sweet.

I've been looking to buy the Maui Waui strain.