Portland, Oregon has a couple of places for Surefire lights, but not many spare parts.
The gun stores are your best bet, in this case Northwest Armory has a good selection of Surefire lights and less on parts, while Keith's Sporting Goods has in my opinion the best selection of Surefire and Streamlight lights and a few more parts. Keith's has some lights hanging up on the walls if you don't see them in the Surefire floor display. Both of these are more or less off the beaten path of downtown portland, but max 1/2 hour east of Portland for Keiths, NW Armory is closer. Keith's is ideal if you are going to see Multnomah Falls or other scenic waterfalls along the Gorge during your visit, he's closer in that case.
GI Joes Sporting Goods has some Surefire and Streamlight options, along with some Maglite/Pelican and cheapy brands. Gi Joes is changing their name to just Joes, so be aware of that change when you arrive. They have Surefire lights behind the counters, but not a really wide selection, but if you want a Surefire M3, they have them mismarked at $225 instead of $252, so some possible savings there and remember there is no sales tax here in Oregon! So save a big purchase for this destination.
REI sells mostly Pelican, Black Diamond, Petzl, Princton Tec, Photon, Mag Industries, Gerber and Innova lights, but most of their inventory is weighted towards climbing headlamps or tiny keychain lights. No Surefire, but certainly worth a visit.
Target stores are good for Inova and Rock River lights, along with some other cheapy brands.
For specialized parts I would stick with online retailers
