could you not experiment at this.... and call a stone to you from the area in this park, that is near to you?
I did this recently really feeling the need to have a hagstone but never having seen one in the area. I called and it came to me. It's worth trying.
Definitely works, IMO. I recently called hagstones back to me because I had lost my entire collection of them, and I've been finding them everywhere. Picked up another large one at the creek last weekend, and found several more that I didn't bring home. Found an awesome little one in a driveway too. lol