" Depends on the motor. Many i
" Depends on the motor. Many inboard motors are marinized versions of what is generally a plain old ford, chevy, or dodge 4, 6, or 8 cylendar engine. If this is the case you could very well pick up all of the parts you would need to convert to electronic ignition at a regular auto parts store such as autozone, napa, discount auto, .... the list goes on and on. However you should keep in mind that the conversion requires more that just the distributor.
You will likely neeed an electronic ignition control module (the precursor to the computers that control auto systems today), a coil, the distributor/rotor/cap, and possibly a different set of wires.
Another consideration is that while electronic ignition offers a slight improvement in performance a typical failure in the system will render the engine dead. Unlike a point ignition where a set of points on their way out can still get you home, when electronic goes it goes without warning.
Unless you really want the little bit of extra umph, or you just have an aversion to point ignition, my own personal thought on the subject is that the point setup is a better route. That is just my own thought. I know there are a lot of folks that have used electronic for years with no problems, but if you go that way a set of spares is a good idea. "