Since Ivey closed up shop, nobody does. It is a real problem. Panda has stated that they are looking into but do not currently process 4X5 C-41 or E-6. I believe Panda will do B&W.
Since Ivey's closing, I've used Newlab in San Francisco and R&R Custom Color Lab in Spokane. Both are excellent in quality and service, but I am settling on R&R for the lower fees and Fedex charges (Spokane and Seattle are in the same Fedex zone).
It might be time for a Jobo (or equivalent) processor. I bought a Jobo Autolab 1000 off ebay 3 years ago. It was the best investment I ever made. Mix up some Kodak E-6 chemicals and you're good to go. A sheet of 4x5 E-6 used to cost me $2.75. I now spend 0.60 to 0.80 cents per sheet.
Lab prices have gone up in the last few years, and if it hadn't have been for this processor, I would probably not be shooting 4x5 anymore.