Blower motor 4320 is a universal part. A quick search for BM4320 found them for sale on Amazon, of all places.
because it is a three speed motor it is not a plug and play replacement for the original single speed motor, that derived its two speeds through the use of the ceramic resistor
other than using my suggestion of a DC motor controller, there are other options out there on how to wire three speeds. Sorry but I could not find them with a quick search
Larry