I would like to obtain and become the sole distributor of a product/service that is patented in the US. What is the best way to go about this?
After you do some homework call up the inventor/owner. You can look up the owner (assignee) from the google/patents page for the patent. If there is nothing in the assignment database, then the inventors are probably the owners. By looking in Public PAIR at the USPTO you can see the inventor's address and the current official correspondence address. I would check to be sure the patent is unexpired has not been declared invalid or unenforceable by a court and the maintance fees are paid.
Depending on how exclusive you want to be (geographical or field of use or time-limited or completely exclusive with the right to go after infringers) you and the owner might consider you buying the patent outright.