I really like the sound of this idea. I was looking to build a car float type thing for my upcoming On30 (O gauge narrow gauge) layout I'm hoping to start soon but all the parts I wanted were in America. Basically the kinda stuff I needed were tie downs, rope bollards, steering wheels etc and I think those would be applicable to any type of boat. If you need general ideas for stuff for little boats might be: lobster traps, oars, bench seats, rudders (if your modelling full hulls), Various wheels and oar locks maybe. I hope these ideas help.
All the best,
Lloyd