I am not sure if this is their preferred email (I got if off the AquaBid account page), but when I bought dwarf crays from Apistofishguys I received some really nice blues. I don't know if they can accommodate an order for 50 such crays, but if wouldn't hurt to ask. Here's the email - apistofishguys@yahoo.com
Second option it to select "Ask seller a question" on one of Pioneer's auctions - http://www.aquabid.com/cgi-bin/auction/auction.cgi?fwinverts&1412698112
That seller regularly offers dwarf crays and the picture shows that some of them are blue, although maybe not as blue as you want. I would contact the seller and ask about nice blues in particular. Perhaps you can arrange an order.