You will be VERY lucky. My Superspec had a leaking sump when I bought it, for the same reason, the previous owner had grounded it. Every breaker's yard I went to burst out laughing when I mentioned the Rover 'T'., said they hadn't seen one for years.
I searched on E-Bay, the Rover forum and everywhere I could think of with no luck. You might have to finish up buying an old Rover 420 just for the sump. But be VERY careful, as you want the alloy sump, otherwise you will have zero ground clearance, and you have to make sure it is from the non-turbo engine and also not from the diesel version, the sumps are all different.
I finished up getting mine welded and although it still leaks, it isn't anything a piece of cardboard and a towel on the garage floor can't cope with
You may have joined too late to see the article I wrote in 'Boys in Hoods' about the foibles of the Superspec, one of which was the ridiculously low ground clearance. After I had mine welded I wound up the front suspension about an 1" and fitted a sump guard from some scrap stainless steel. See http://the-superspec...ustment_10.html and http://the-superspec...sump-guard.html Since then I have had no problem at all.
Al