Joe, further to Jim's suggestion (because the School of Scottish Studies no longer exists per se, having been subsumed into the Department of Celtic Studies -- I think), a quicker way might be to approach either Steve Byrne or Chris Wright via the Kist o Riches website.

Each of these admirable chaps has been involved in the work to preserve Hamish's archive, and would also be able to put you in touch with Hamish's widow.