I know that we do, or at least at one point did, sell the coupler bushings. I have a pair of them at home right now, a door-prize from last year's Mid-US Ramble, donated by Pelican Parts. If you don't find them in the catalog, try calling 888/280-7799 and asking the sales guys about price and availability.
Mark, you'll also have to remove the front shift rod (or at least the gear shift lever) to replace some of the bushings on the tail-shift linkage. I don't think you have to dig into the tranny itself.
One way you can try to find where the slop is--grab the part of the linkage that goes into the transmission. Have someone wiggle the gear shift lever around. Look for parts that are moving. In between the parts that move and the parts that don't is where you'll find slop. There are often bushings in those joints--replace the bushings.
You can repeat the test for various parts of the linkage by grabbing parts that are further forward and holding them still while looking for movement in the rest.
--DD
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Pelican Parts 914 Tech Support
A few pics of my car:
http://www.pelicanparts.com/gallery/Dave_Darling