few places (if any) in US or Canada will rent solo due to insurance reasons
All floatplane training facilities in Canada will rent solo for the purpose of the rating, as one hour's solo is the minimum legal requirement.
I did my floatplane training at
Elmhirst's Resort, and would recommend it. The current cost of the basic rating package is C$1099 (= £489 at today's exchange rate); accomodation was a lakeside cottage that my wife and I both liked very much. There are many other good places in both Ontario (see
list of seaplane training schools), and British Columbia.
Beyond the rating, it can be difficult to find places to rent on a solo basis; but it is certainly not impossible. I believe (could be wrong) that it is considerably more difficult to find such places in the USA, compared to Canada. One place relatively near me that allows solo rentals is
Algonquin Flight Centre (Citabria, C$150 per hour, local solo flights permitted after completion of bacis course, x-country solos permitted after 15 hours and checkride).
If you are keen on time-building, my advice would be to sign up for a 50-hour "bush-flying" course. See for example
Georgian Airways.
Some resources:
Flight Test Standards & Guides - Aeroplane
Instructor Guide - Seaplane Rating (TP 12668)
P.S. You may find
this thread to be generally helpful.
FAA Seaplane Flight Training Handbook