Collecting?

[Vagineer1]

Where can I find a Pink Diamond? I need one to create a simbot.

[-Fields-]

It spawns randomly, use collection helper to spot them, you might be lucky to pick one up at the pawn shop to.

[cruinne]

Random luck is how most people find it. There are various things your Sims can do which increase the chance, but most are not simple/easy/quick:

• (Requires Ambitions) Get good at Inventing, and create a Miner. Digging outside with the Miner object increases their chance of finding rare gemstones.
  
  
• (Requires Pets) Get their pet to find it. Dogs can go out treasure hunting and when their skill is high enogh, they will bring home rare gems.
  
  
• (Requires World Adventures) Become a master board breaker. Using the board breaker to break space rock will sometimes produce a pink diamond.
  
  
• Put extra tills in the pawn shops. Each till should have its own stock, and pink diamonds sometimes show up in the pawn shop stock. More tills means higher chances of that happening.
  
  
• Go through their neighbors' trash -- for some reason, your Sim's neighbors sometimes throw away pink diamonds.
  
  
• Explore the mausoleum in the cemetery. They''ll sometimes come back with a pink diamond.
  
  
• Cheat. Put your game into cheat mode, and place a rare gem spawner, then just wait for the Pink Diamond to appear.

[Quietus Reaper]

You can simply look at a screenshot of your towns map online showing all the pink diamond and other important spawn spots. They only pop up in a few places so collection helper is overkill if you just need the one.
http://www.carls-sims-3-guide.com/sunsetvalley/
That is the locations of pink diamonds life fruit etc of sunset valley. Enjoy