There's nothing special about shipping internationally. You package the same and the USPS ships by weight. First class international mail ships up to 3 lbs. After 3 lbs. the rates get pricey. Most of the quilts weigh less than a pound though. You can get an estimate of international postage costs at:
http://ircalc.usps.gov/
For example, my January quilt weighs 6 oz. packaged. If I send it to California it will cost $2.07. If I send it to Italy or China it will cost $5.64. Not a huge difference.