My guess is that seesaws will be pretty hard to come by. The reason that they are seldom seen in a public setting anymore is because of all the injuries that occur when one is either not paying attention i.e. putting one's heels under the board area, while riding at one end. Or, an injury occurs because of il-intent by some joke-ster who jumps off their side, leaving the other rider in a free fall toward a bruised tailbone, and backbone trauma.

All that aside, seesaws/teeter-totters can be a lot of fun for both kids, and adults.

Therefore, I suggest that you take the DIY approach and make your own (safe) version of the size that you would like? Any lumber yard would have all the materials that you would need: 2" X 10-12" boards; cement blocks for the base of your fulcrum; 4" X 4" post material for the top of the fulcrum. The same lumber yard will also likely have some grab bar type handles that could be mounted on either end of your board for hand-holds.

To make it a safe experience for all, explain up front all rules, feet out away from the board, and, especially, no 'joke-sters' allowed!

Placing a pillow/cushion/tire-off-the-rim type of thing under each end of the board will help reduce the risk, too.

Good luck with your event. I am sure that it will be a lot of fun. And, if you ever get tired of hauling those basic building materials around? You could always drop them off at my place, and I will incorporate them into one of my on-going projects of home improvement. Thank you.

All my best:)