The easiest way to get the pink diamond is to watch the map after being given the Op. to make a simbot, It will be pinpointed, but you could have to wait several days.
Alternatively, the second easiest way (that I know of - I don't own all EP's) id to buy it from the consignment store. If they don't have one, buy everything in the store forcing the store to restock. You may have to do this several times. (This is cheating, but, you could put a couple of extra tills in the consignment store to increase your chances.)
Learn how to split space rocks with the martial arts skill. The more skilled. the more frequently you will get a gem from splitting the space rock. Pink diamonds are rare, but I have obtain a good number this way.
Buy a miner from the consignment store or make one on the invention bench. Mining will occasionally find a pink diamond.
Lastly - cheat. Place an epic gem spawner on or near your lot, using buydebud, and wait. Again, it's a rare gem so you may have to wait a while.
Finally, I have seen a set of maps showing approximate pink diamond spawning places. I think it was in "The Sims 3 Guide" on this site. The only other site I go to that could have the maps is the official site.
