I looked into this for my car but the short answer is you can't find anything new any more.
I was tempted to buy some from another car with similar size discs and modify to fit but I haven't tried it yet
The MG Rover part numbers are SMD000080 (RH) and SMD000090 (LH) - there are some on ebay but the prices can be a bit silly
If yours are not totally rotted away you are probably best off removing, soaking in some evaporust, good wire brush session and then painting them yourself. I fear that due to the age of the cars they might be too far gone though (the ones on my 2010 accord are too far gone for that and that's 10 years newer!)
Cars that i've found being listed as cross compatible if it helps your search:
Rover 200/ 25 / MG ZR
Rover 400 / 45 / MG ZS
Integra DC2
CRX
Del Sol
EG/EK Civic
Many of these cars came with rear drums which might be part of the problem. It seems like it's a lot easier to get front ones, for now at least.