What? I bought a reman transmission with all new internals for my series 3 earlier this year. My new fuel pump is on the way. I put new axle shafts and drive flanges in my rear axle last year. Same with all new wheel cylinders and brake shoes. You can order complete galvanized chassis and body parts. The engines just last.
Or you can get yourself a mid 80s defender. That way you can get new factory parts. Just costs an arm and a leg.
Parts are still readily available here in the US. You ain't going to get it at NAPA but you can order it. Roversnorth and the like have all that crap...and in stock. Or they can get it.
Or if you are savvy, you can call England and order parts. They only have 6,000,000,000,000,000,000,000,000,000,000 crap tons of rover parts.
Get yourself an Austin Gypsy. Then you'll know what "rare" is.