I believe that A&I in L.A. can take 4X5 via mail. call them...
also, Carl's Darkroom is VERY FAST! i shipped the film (4x5 and 120) e6 via USPS Priority, and I had it back in my hands within 4 days or so. Very accomodating, and very friendly people. Pretty reasonable pricing as well.
here's their number (they're in Colorado)
I use Duggal, which still seems to be doing a consistent business in processing color sheet film. They take orders by mail, but you may need to call them to set it up and find out how much they charge and such. Contact info at www.duggal.com