i hope this helps, but yesterday i saw 2 waterway fins on ebay. like the other poster said, it does take a while to make them, and i don't know of many/any places that have them already made.
the auction ends tomorrow, if it's the right footpocket size, you can email the seller and see if they'll expedite shipping. since it's through ebay, perhaps the cost of faster shipping may be offset from the cheaper price.
just do an ebay.com (not ebay.co.uk) search for *monofin*.. i just checked and both are still up for auction.
also you can try
http://waterway.dk .. it's a danish site that (i'm guessing) is a reseller for waterway. maybe you can contact them and see if they have them in stock or do they turn around and place the order with waterway.
good luck.