Is there a way to become a college instructor/adjunct without a master's?

College level teachers have at least a masters degree that should be related to the area that they are hired to teach. Many hold a doctorate even at the part-time level because they can't get full-time positions on tenure tracks. I am not aware of any specific law requiring at least a masters, but I would expect that it would be in the policies traditionally adopted by colleges by their own Boards. There is no college level certification.

I taught part-time in a community college and hold a masters degree.

Colleges will require a minimum of 16 credits at the graduate level in whatever field you want to teach, which usually means at least a masters and often a PhD. For a part-time job that pays less than minimum wage and doesn't include benefits. Colleges do not require a teaching certificate, nor do they care if you have one. Teaching experience (at the college level) is good but not required, at other levels doesn't really count very much.

No. You have to be better educated than the people you're teaching.

The federal government does not make rules telling schools who to hire.

My board of regents has a rule that people must have 18 graduate credit hours in the subject they want to teach. That only applies to graduate teaching assistants. That is, if you are in a graduate program and have credit hours in the subject, you may be eligible for an assistantship where you teach freshman courses. Our full time instructors (non tenure track, contract positions that pay reasonable well and come with some benefits) you have to have an MA or a Ph.D.