RE: 1/16 sherman on landing craft
Hi tomo 17, I am in Australia so it is a bit hard to put you on to someone that might be able to help with the parts you are after.
I always seem to have good luck with Ebay, type in RC boats or Scale boats and see what comes up.
The cordless screwdrivers I used were 12 volt so I can't comment on your 3 volt ones.
My landing craft was my first boat so I am nowhere an expert on them. there is a very good forum here on RC Universe I think it's called
" Scale boats" Have a look there and see if they can give you the information you seek.
Let us know how you get on.