Not a swap, but at one gym where DD competed, they used to allow the booster club to host a used leo sale 4 times a year. Leos had to be dropped off on Monday, and picked up on Thursday, or they were donated to charity. The sale took place Tues & Wed.
One condition of the sale was that gym personnel did not have to deal with it at all. As such, the booster club staffed a table, so $1 was added to the price of each leo, and baked goods were sold those days too. Not a huge money-maker by any means; but it was an easy fund raiser that brought in a few dollars, provided a nice service, and worked quite well... until the gym owner got greedy and demanded a cut of the action (to the tune of $5 per leo sold) That ended the used leo sale in a hurry.
Some concerns I've heard gym owners voice when approached with leo sale and/or swap idea: selling or trading used leos cuts into their pro-shop profits, the appearance of used leos always sitting around the gym, paying office staff to deal with making change, answering questions, etc.
Just a couple of things to think about while brainstorming how you might want to put your plan together.
Good Luck, hopefully you'll be able to work something out.