Good luck with that. If mailed they'll think it's junk mail, if handwritten, they'll think OMG someone's been kidnapped.
You gotta meet people in a setting, either professional (work related) or casual: church, ball fields, social events. Cold contact, letters, surprise door knocks just are awkward.
People have to already know you a little to be able to commit to something as granting you free roam of their property nowadays. Folks have a mistrust of strangers thanks to scammers, telemarketers, swindling salespeople and now thanks additionally to lawsuit happy blood suckers.
Hate to be a negative Nancy but you have to cultivate relationships. It make take you 2-3 years of showing up for some annual event and getting to know some old timers, help with a community cleanup, become a mason, do volunteer work. Then slowly but not pushy inquire within about these things.
I was one of the few people who would give a certain guy at work the time of day, just being kind to the dude, he scrubs toilets at work and sprays w-d40 on hinges. Everyone thinks he's insignificant. I have no idea anything about the guy, he knows I hunt- he asks me about it, I invite him to hunt with me- next he wants me to come to his property and give him my opinion. I know the guy for 3 yrs, never knew he had land of his own. Fella makes $9 hour, scrubs commodes, owns 1400 acres. And wants me to hunt with him. I didn't even ask about it.
Long story, be open- talk to people, don't be a snob or a smart butt about things. Share life, share kindness, share Christ and God will reward you. Cultivate