does anyone know the type of electric motors used inside of a trolling motor,or where to buy one
Custom motors
For the lasts 20 years or more electric trolling motors are purpose built by the manufaturers. You could order an armature from their parts department and get paermanent magnets and your own housing and make a homne brew motor I guess.
Most folks just by the lowest cost motor in the power they need and cut it apart and fit it to their boat. If you are not really good with electronic speed controllers then you may want to get one of the motors with a variable speed drive using a pulse width modulator to control the motor voltage. Getting the motor and controller all in one package is really less than trying to make it yourself. They have all the economies of scale working for them.
Check the Cabelas
marine 2006 catalog. They have on page 51 a few motors that mount on trim tabs. You might be able to use one of these. Or do a web search for “engine mounted” or “trim tab mount” trolling motors.