Has he (the mechanic) given you a list of parts?...
Some may not be available via Honda suppliers but many should be found via other sources..
E g cmsnl.com
What are the issues..bent valves/burnt valves??
You might consider the Vince&Hyde cam chain tensioners and guides....better than stock and easy to fit with head off.....
Others to try..David Silver Spares, Randakks cycle shack, Vintage CB750(Canada)