My C300 viewfinder got damaged recently and I have now bought a replacement part from a Canon Repair centre in the UK.

The company is called H Lehmann, they are really professional and helpful, and also do CPS repairs. For anyone in the UK here is their website URL.

Camera Repair at H. Lehmann, Canon Repairs, Nikon Repairs Centre, Canon CPS Professional (http://www.hlehmann.co.uk/)

They sent me a PDF with the C300 external spare parts listed.

A word of caution that repairing your own camera could void any Canon Warranty.

H Lehman are where I was able to source the little rubber covers for the various sockets (headphone AV etc) that fall off as soon as you look at them. When I called they know all about the frequency with which these covers need replacing as they were apparently highlighted in the parts list that they were referring to. Two covers were £15 delivered.

H. Lehmann Ltd
247 – 249 London Road
Stoke on Trent
Staffs
ST4 5AA
Telephone: 01782 413611
Email: service@hlehmann.co.uk