First, are you sure that you can provide a LIFETIME, LOVING home for a pig? Go here to find out!
Select the state you would like to adopt a pig from. If that state does not currently have any pigs needing adoption, try some of the neighboring states. Many sanctuaries are willing to work with you with regard to transporting the pig, often across state lines, if the pig is assured of having a good, "forever" home. Each state has different requirements for transporting animals, however, so you'll need to discuss this with the sanctuary, to ensure that all of the necessary paperwork and/or bloodwork has been completed.