Only thing I can suggest is to put a rarity 99 item into the shop wiz with 100000 as the minimum price and see which of those people that come up are rarity 99 collectors. You might also want to try plushie collectors--but only those that have magicals in their collections. Some plushie collectors (like me) don't even bother with the magicals because they are too darned expensive. And, definitely try anyone who is collecting yurble stuff--that might be your best bet, in fact. There isn't a whole lot of yurble stuff out there so they might be more willing and financially able to buy a magical.
Tested made this fabulous set for me!!! Isn't it great?