MD22 engine is a rebadged and repainted Perkins Prima M50 engine (also found in the maestro and montego cars), this is correct. But you would be wrong to assume that the water pump wasn't changed by Volvo in the process (or a few other things). Here's how I know this, I have a Volvo MD22P (Same engine apparently) and I have a different water pump than your picture (mine has the inlet and outlet at a 180 degree angle) so I know that they changed mine. I also know that other MD22 oil
filters don't fit my engine (ask me how I know)!
So, that's the bad news (and you've seen the Volvo price)! Your water pump is almost certainly a Jabsco
OEM, so perhaps you can find it in a Jabsco
catalogue, but it took me a while to hunt mine down, and still it wasn't available easily.
But, the good news is this, the pump shaft has a typical failure mode where grit gets under the bearing seal and destroys the shaft surface, resulting in it leaking water all over the engine. It's not too hard to fix. I even have a link for you: Volvo raw water pump repair
Alternatively, you can probably take the shaft to a machine shop and get one made up in stainless steel
for less than the cost of a replacement pump.