The "Design: Rhinestone Sunglasses" is one of the rarest items in the game, and getting one on your jewelcrafter will definitely get you a lot of gold, since you will be able to craft and sell as many Rhinestone Sunglasses as you want. These sunglasses can sell for several hundred thousand gold, and creating them will only set you back a few hundred gold. In other words, these will give you a huge profit!
The only problem is that getting the Design is difficult, and it requires a huge amount of luck or dedication. The design itself can drop from any mob from either Cataclysm content or from any mob from the Mists of Pandaria content. Basically any mob between level 81 and 90 can drop it, but apparently it has a much higher chance to drop from Cata mobs.
People who farm for it prefer to focus on the Cataclysm rare world bosses, since these has a rather high chance to drop the recipe compared to all other mobs. Download NPCScan and add the following information to the add-on:
/npcscan add 50063 Akmahat
/npcscan add 50089 Julak-doom
/npcscan add 50056 Garr
/npcscan add 50009 Mobus
/npcscan add 50005 Poseidus
/npcscan add 50061 Xariona
As you can see from the macro, Akmahat, Julak-doom, Garr, Poseidus, Mobus, and Xariona are the mobs you want to farm, and each of them are on a 4 hour timer. These rare mobs can spawn in all the Cata zones, and I suggest checking them up on Wowhead to see which one you prefer to farm. I would advise against Poseidus since it will have a very high amount of competition, since he drops an BoE mount that sells for a lot on the Auction House.
Remember that you need to have Jewelcrafting as one of your professions to even be able to loot it! The design itself is BoP, so make sure to farm it on the correct character.