However they want me to sign and notarize it.

We were looking into a very small mobile home park (5 leased hook-ups, 4 leased park-owned units) and contract required tenant estoppels (where tenants sign a notarized documents stating that the property is in working order, the leases are accurate, there are no side agreements, no money due from seller, etc etc).  

Not a problem, but when you're closing in 30 days and they have to send it to you, get notarized, and return on time; well there's a lot that can go wrong.

If not, are you able to find anything else locally that makes sense?

Like smoking, it is very difficult to go back from a pet property to a non pet property without significant time and cost.Applicants who avoid the extra compensation or play games to qualify, legally or not, are not desirable tenants. 

If not, are there other investors in the area that would be interested in making this happen?

I had the document looked over by a lawyers office and we met at a notary to get the document notarized so that there would be no question in the future.

Can i just go online and find a promissory note and mortgage template, write it and get it signed with all my stakeholders (lenders), or do I have to find an expert (or is it an attorney) and get it signed/notarized via some state authority? 

This is pretty standard when buying a tenanted property.You also want copies of the lease and make sure they are notarized, so you know the information is correct.

We had to print, sign, and notarize a good amount of paperwork before we were able to close.