I encountered the same thing ... discontinued.
My boot was intact where it wrapped around the shifter, and also intact where it was vulcanized to the metal frame, but completely separate between the two.
I originally conceived tis to be a rather hillbilly solution, but it seems to be holding up well... I pulled what was left of the boot and set it on my workbench, and used saran wrap top and bottom to form RTV gasket into an ugly but serviceable bellows repair.
1. ) I folded some saran wrap to rougly match the bottom side of the bellows, and goo-ed it to what was left of the bottom of both parts of the rubber, trying to form the saran wrap up into the creases where possible. You'll wind up with folds in the saran wrap -- that's not important -- what you're trying to do is reverse-engineer a bottom mold to retain the RTV.
2. ) Let the RTV dry/cure to hold the 'mold' in place.
3. ) Spooge the RTV liberally on top of the saran wrap, trying to fill in the holes in the old rubber and put a thin layer on top of the old rubber itself (reinforcement).
4. ) Lay another layer of saran wrap on top of the uncured RTV and use it to *gently* manipulate the gooey RTV into the shape of the old bellows (be careful not to press to hard -- you don't want the saran wrap to be the only membrane, rather, you want a saran/RTV/saran sandwich).
5. ) Let the RTV cure.
Repeat 3, 4, and 5 as many times as necessary to build up a 'replacement' rubber bellows. I thought I'd be able to peel the saran and just have RTV left, but it seems to work out equally well to have three alternating layers of saran and RTV serving as a flexible composite.
For extra style points, use black RTV -- it will still be ugly, but at least it will match. If rice racing is your thing, consider alternating blue and grey.
Hope that helps -- it is holding up quite well on my truck.
Randii