I'm not familiar with the Williams Treaties (my own work focusses on the
nineteenth century), but I do know that government-generated material on
Indian treaties is available at the National Archives in Ottawa in a group of
records called RG10. Last year or so, the National Archives Indian Treaty
Project microfilmed about 500 documents relating to surrenders, adhesions and
amendments. They are on reels T-9938 to T-9941, and can be borrowed
through interlibrary loan. Other documents would be available in other
parts of RG10. You might want to telephone the archives (let the
switchboard know that you have a question about RG10, and s/he will put
you through to the right person) at (613) 995-5138.
Isn't John Milloy at Trent? I'm sure he'd also be able to give you
some leads.
Best of luck,
Dave McCrady
History/University of Manitoba