grinding first and reverse

I need help with my tranny. I grind in first and reverse unless I make a smooth transition from 2nd to first. 2nd and 3rd don't really grind at all. It's a 3-speed manual with a 200 c.i. engine. If I'm in neutral, it doesn't matter how long I hold the clutch down, it still doesn't slow down enough for me to go to first or reverse. I even tried turning down the idle mixture on the carb but it still grinds. I have changed the gear lube also. I think I need a new clutch because the clutch pedal won't return to it's original starting point unless I put my foot underneath it and pull it back up. The only problem is I can't find clutch parts for a 65 Mustang with a 3-speed. Any ideas?