Welcome to the forum! Here is a link to the very top of the forum.It has links to several different parts supplier. There is also an thread with a free download of the Factory Service Manual for your bike. More than likely the FSM will prove very handy in your restoration project. VintageCB750.com and partsnmore.com are two places I do most of my shopping. Good luck with your project!
parts suppliers:
http://honda-cb750-s.456789.n3.nabble.com/Parts-sources-for-our-cb750s-Updated-with-a-little-dohc-and-electrical-6-3-10-td462672.htmlFSM-Factory Service Manual:
http://honda-cb750-s.456789.n3.nabble.com/NEW-Repair-manuals-April-26-2011-Updated-td685918.html