My starter had that issue in my 305 v6 and I had mine rebuilt locally. If you have someone local or in the area that can rebuild starters you'd be good to go.
Have you been able to check all the electrical connections to the starter though? Loose wire will cause those problems.
Edit: I don't think a new one is available, unless the 305 v6 starter in the same. If you can supply some pictures I could check with my local parts store. Last I check 3 different bolt patterns were available. Two of which may be the "Big truck style" if there's a difference.