Well, you could start with Accuspray but I don't think you will get much help there. If you need fluid pressure lines they are kind of universal which can be gotten from any paint jobber in custom lengths. If you have internal problems with the turbine you would have to open up the turbine box and determine who's motor they were using. Now about 90% of these motors are Ametek motors made about 2 hours north of me here in Ohio. They do not sell direct however they have dealers everywhere... go here... http://www.centralvacuummotor.com/lighthouse.htm
Go all the way down to the near the bottom of the listings and you will see 3, 4 , and even now the 5 stage replacement motors. Whole replacement motors start at about $159 all the way up to $259 or so. You can also occasionally find used turbines on ebay if you can match up your numbers.
And yep, the 4900 is hands down better because it is definitely a 4 stage unit pumping out 8 p.s.i. at the cap and this is just an opinion....it has a better gun which takes advantage of the extra pressure/cfm.