General stuff: I have had good luck with Revezilla.
Also keep a eye out in Swap meet in this forum.
Shameless plugs for my favorite Moto Guzzi Resources.
Revzilla: I ordered the wrong speed bleeders. NO hassle return for full refund. No restocking fee. Kid on the phone also reminded me that I had store credit from previous purchase so saved me 5 bucks and threw in free shipping.
Curtis knows his stuff. Help is just a phone call away.
Spent 15 min on the phone trying to find adapter for my Tom Tom. Cross checked several models, but no go. Parts guy made the extra effort.
Mike Haven can fix anything.
Another knowledgeable source for parts.
My local ACE hardware store.
Robert has extensive knowledge of obscure metric fasteners.
My local O'riley Auto Parts.
Good for the common stuff.
Local motorheads and friends Charlie and Phil.
And of course members of this forum especially my BFAM Dusty-my MC consultant and life coach.