That split sleeve is just pushed up against the back of the ear on the alternator by the washer and nut on the bolt - only a friction fit in the hole in the bracket, so the torque on the nut can move it.
Put some PB Blaster on the sleeve and work it loose toward the rear with a pair of channellocks - it WILL move once you break it loose, and the alternator will separate from its grip.
Look in the Yellow Pages under "Auto Electric" or "Starter" for a local rebuilder; they're usually mom-and-pop operations. If you can't find one, just get a rebuilt to use temporarily while you send your original to Pirkle.