As is the nature of the Web, sites come and go, and contain varying amounts of information. These are the ones I find worth keeping an eye on.
1 Mamiya America Inc. ( http://www.mamiya.com ) has a web page with a User Forum for older cameras which includes considerable discussion on the TLRs. They can supply manuals for some models (C3*, C33*, C330F*, C330S, C220F (*photocopies)) within the USA only. There is an entry in the Forum about obtaining manuals. An online version of the C330 manual in Portable Document Format format is available. A similar facility is provided by Mamiya UK ( http://www.mamiya.co.uk ). The various Mamiya agents have been posting revised history documents in the past year or so that under-play or ignore the Mamiya C series.
2 The Medium Format Digest ( http://www.exeter.ac.uk/mfd/ ) archives an the University of Exeter have finally been removed. The new database-supported Medium Format Digest is at Photo Net ( http://photo.net/ ).
3 Further Mamiya TLR information can be found on Jan-jaap Aue's home page ( http://www.lighthunter.com/ ) . This includes scanned manuals for the C220 and the C330s.