There are several outfits that can do a proper, old school blue. simonp is right to recommend Turnbull -- they're probably top of the heap, and can do a variety of bluing styles specific to manufacturer and era, too. You will pay top dollar for their work.
Glenrock Blue also has a stellar reputation. Ford's is still considered quite capable, too, though with a spottier record of late than it used to have.
Most quality local gunsmiths can do a decent standard hot salt blue if you're just looking for something basic and don't want to spend restoration prices.
A forum community dedicated to 1911 firearm owners and enthusiasts. Come join the discussion about other firearms, gun ownership, gun care, tactical firearms, small arms, optics, gunsmithing, styles, reviews, accessories, classifieds, and more!