Last I knew, the Sportsman's Warehouse in Anchorage, AK still had some Ultra Mags. You might talk to the folks at you local store and see if they can get them for you (or from another store). There were some that got moved from one of the Colorado stores to another...but I can't recall which store wound up with them. You could go to http://www.sportsmanswarehouse.com/stores_all.htm#ak and just start emailing store managers (listed in the store locator).

The .504 G-series, 97 Whitetail, 98, Lightning, Bison, Super Safari, and any of the Super91s should be legal in Washington. Aside from not being legal for hunting there, the Thunderbolt is a good one to avoid for other reasons.