Looking for advice on which address I should send a "I want to buy your house" letter to. 

I have sent letters, but phone numbers are not available for all but a couple. 

I have proof they did not, both bills and a letter from the utility stating they never transferred service.

Do you do yellow letters?

The smaller parks are generally owned by a now aging senior population who are not the least bit interested in emails or campaign letters.

For example, one great idea is if you drive or walk by a house that looks like nobody lives there, figure out who owns it (usually the person actually has another address), and send them a letter.

Without trying to sound too misleading to the seller i would either in person or in letter explain to them that I'm not a realtor, and that no seller fees would be required to finding a buyer which i guess is slightly deceptive.

The chances of BofA talking to you are slim unless you had seller sign a POA and/or 3rd Party Auth Letter. 

Write them up a personal letter with a pic of the home in its distressed condition.

Naturally, I'm thinking 'I need to send her a letter'.