1) Look up local universities and email the chairperson of whichever programs relate to the type of cofounder you need (i.e. electrical engineering, marketing, etc.). You could even possibly go there in person and put up a sign on a bulletin board.
2) There may be relevant Meetups in your area, go there and network with attendees (www.meetup.com).
3) If you're specifically looking for engineers, look up local 'hacker' / maker spaces that may exist in your area (see here: https://wiki.hackerspaces.org/List_of_Hacker_Spaces).

Send me a message if you want to discuss more options and how to access them,

all the best,

Lee