Canon 10D or Spotting Scope

Currently I have an Olympus C2100 but it just doesn't have enough zoom. I take pictures of wildlife and birds. So I'm trying to decide if it would be better to go with a Spotting scope with a focial length of 460mm that I can attach my C2100 to. Or buy a 10D.

What kind of lens would I need for the 10D? 75-300mm? Has any body every take pictures with the 10D and a 75-300mm with out a tripod and got good results? Where can you buy used Canon lens?

Thanks.

Carl