Drive Shaft

[David]

These appear to be rarer than hens teeth!
Any ideas where I can obtain one? Are they standard Mustang shafts?

No they are not Mustang.
First define the problem, please. If it is reluctor rings, then they are available at a price
https://www.reluctorrings.com/cars/rover (look for MG ZT 260 rear in the list).

If CV joints, contact Austin Garages who may be able to help, again at a price!

If the shaft is bad (as in accident damaged), try calling Redditch Vehicle Recycling about the shafts on #125 currently being broken by them. Tel: 01527584567
One of those shafts may already be damaged though, judging by some of the vehicle damage photos (or already 'spoken for').

David