There are a few parts available for the 4900. As per the CompassMicro site, I see they have the "pump unit" (pump, capping station, wiper blade assembly), "ink selector" (damper assembly), and "roll paper adapter" listed- though you can also check the exploded diagram for a more complete listing of parts they can get, and call for pricing/availability of those parts.
You can get the Service Manual with parts list, and Adjustment Program from www.2manuals.com. The Service Manual specifies how often parts should be replaced, how to troubleshoot issues/errors, and instructs how to replace parts. As with any machine, proper maintenance is key to the best performance and longest life.
Best regards~ Dana