Before buying or selling seeds, check with APHIS to see if they have special requirements or qualify for the 12 or fewer exemption.
www.aphis.usda.gov
I'd recommend going with commercial businesses instead of a random person to avoid potentially hefty fine and the seizing and/or destruction. If illegally imported plant material makes it to your property and it is discovered, you will be on the hook the payment of all inspections, mitigation, destruction, and restoration of the natural environment of the surrounding area.