Here is a reproduction, no individual parts available that I know of. PG Classic 114-70KIT Mopar 1966-70 A, B-body Automatic Console Shifter KIT | eBay
These shifters were never tight, the same shifter is used in my 67 Barracuda and it is the way it always was.
I'm not sure what could wear out on these or what you could do to tighten them up.
The bushing in the transmission bracket could be loose or missing, the filler strip at the top helps the rattle.