I did a bit of a search on this, as so many are having a ball finding it since Jabbadashery won't be able to make it unless they get enough people to want it. Zam isn't as popular or easy to recreate, so I don't see this happening anytime soon. After looking into it, I came up with a few site with a listing for purple neoprene. I do NOT vouch any of this is what you want. only that this is what I found. If there is a better site, do list it and maybe we can get someone who judges this costume to chime in with their thoughts.
DK Douglas Company, Inc
Neoprene Closed Cell Foam and Specialty Foam : Water Resistant Fabric : Seattlefabrics.com
Neoprene Fabric | Buy Neoprene by the Yard | Mood Fabrics
(currently sold out, but that could change)
Neoprene Scuba Fabric Polyester Spandex 58" Wide â€“ Fabric Wholesale Direct
Neoprene Scuba Techno Athletic Double Knit All Purpose Fabric Sold by The Yard | eBay
(it's ebay and won't stick around long) also, search purple neoprene fabric/material for other listings)
These are just what a search found. Some are too thin and would need some sort of layering to get the right thickness. But, considering the few options for the right material, this is the best I could come up with.
Hope this helps you new Zam builders.