Well, if you don't want to or can't instruct as a MEI you have to:
(MEI doesn't mean you can instruct due to some insurance policies or lack of MEI jobs. I wasn't allowed to teach multi until I had 500 multi!)

1. get multi flying free from someone (good luck)
or
2. Buy it yourself. Rent or purchase a twin. I knew a group of instructors that got together and bought a Twin Commanche to build time in, and then they sold it. $100K is not so bad went split 6 to 8 ways.