If someone has no intention of selling there really isn't a magical script to convince them. At that point you just try to keep in touch every 6 months and eventually something will break.
Hi, My name is Dave and I was wondering if you've ever thought of selling your park?
IF Yes keep talking, get info, bond with them, be a person
IF NO - thanks, call back in 6 months
It's been my experience most people looking for great scripts are really just suffering from call reluctance (I am not saying this is you). Picking up the phone is half the battle.