The Polaris MSX 150 (and the MSX 110) PWC use a completely different engine from all other Polaris PWC.
Only used for the 2004 model year (and only on those two MSX models), it is a Marine Weber MPE 750 two cylinder turbocharged four stroke engine.
The Weber engine is German made, and was also used on some Polaris snowmobiles, and on the Hydrospace brand PWC.
All other Polaris PWC (including the MSX 140) have 2-stroke engines, and share no engine parts with the Weber engine in the MSX 110 and MSX 150.
In North America, one source for parts and information is Randy at Watcon.com