I had this idea earlier in the summer, as I contemplated buying yet another watermelon whose flesh we would not eat, and wasting all that money for rind: I called a local grocery store that sells prepared fruit plates in the summer, fruit plates that I (correctly) suspected were prepared in-house. I arranged to meet their food manager who covers the morning shift (when such things are prepared) and the produce folks kept an apple box of rinds for me - normally such things are composted by this particular chain.
I won't lie to you: getting that home on my bicycle was hard. I couldn't remember what size an applebox was, and at only 2/3 full, the box was still incredibly heavy. I had a hard time stopping and starting pedaling without tumbling over to one side or another, and I had to make all lane-changes and turns very gently (which is a taller order when one is riding in traffic on city streets on a Saturday morning). It took me 5 hours to peel all those rinds, and my wrist was jangling with weird nerve-pain by the time I was done (I iced and spent the evening in a compression-bandage and had no repercussions the following day), but it was amazing to make SO MANY watermelon rind pickles all at once! I made 22 jars, of varying sizes ( 8-12 oz) this time, in three varieties: normal, not-so-sweet, and spicy.
The best part? Because those rinds were headed for the compost bin, anyway, I got them for free!