Thanks for the info regarding the "magic" price of 5.
As far as a citable source of what a manager can or can't buy, I can only suggest looking at a fund's accompanying documentation (i.e. prospectus, board by laws, etc.). However, I still don't know if you'd be able to find such a restriction listed.
I do know that one of my finance professors had told me (well, the whole class actually) years ago that there are some institutional investors that have such a restriction, and therefore, some companies will do a reverse stock split to raise the stock price, which would then make them eligible for the institutional investors. I think he mentioned that RJR Nabisco did this several years ago.