Hey Mechkiddd,
Go to the "FAQ" section of this site. Someone has been kind enough to post an extensive list of online sources. The "Partsfish" at Powersportspro has exploded diagrams of parts (no part #'s though).
The 75-78 750F bikes are all "Supersports" so the rear brake line you mentioned is the correct one provided that your bike is a 77 750F model. In the USA the '77 750F came with dual front disk brakes, Comstar(not spoked) wheels, a black motor, and other features that make it easy to identify. Be sure of your model bike before ordering parts.
Once you identify the parts you need you can also post them in the "wanted" section on this site. It can be quite a bit cheaper than buying new parts from a Honda dealer.