Found it, Ames Performance Engineering FR 409 and FR 410. It is for a round shift stick but molds to the stick like it was made for the rectangular one.

They sell the 67-68 shift boot and retainer for the rectangular stick, FR 409D and FR 409W. I'll post a couple pics of the one I have, doesn't have the Hurst logo on it.

Too bad you live so far away, if you wanted it I could hop in the car and deliver, don't know if I'm ready to stay in hotels just yet. Be a good excuse for a 3,000 mile road trip.