Anyone have any information on this printer? Like, how to use it, for example? It came as part of the Commodore 64 bundle I got off eBay, but the MPS803 didn't come with a manual, and I can't seem to find any relevant info. on the 'net. Any help would be appreciated.

Here Is the link to the manual your after.
It Is not good quality but readable.
Hope It helps.

http://members.tripod.com/~keithsny/manual803.html

You may find this site useful for parts.

http://www.oldsoftware.com/Commodore.html

Thanks! That's perfect!