Service Manual is available from Triumph. Mine cost $52 from my dealer, but I have seen them advertised for as high as $83, so look around. I ordered the Bonneville Parts Microfiche on CD from here
Fiche-man
and they are now listing the fiche and manual together so you might want to check that out. I do not know if this is the full Triumph Service Manual.
You can get the Haynes Manual for the new Bonneville from Amazon, Motorbooks and I think NewBonneville.com. The Haynes and Service Manual are complementary, both nice to have.
BikeBandit.com offers OEM replacement parts and has an online fiche; however the part numbers are theirs, not Triumphs. Nonetheless, I have found it quite helpful:
Bike Bandit