For the Death Star, I image the Empire just grabbed whatever huge crystals they could get their hands on and shipped them to the construction site. The Imperial military was definately not interested in Sith cult stuff and would rather just get the weapon working.
With Starkiller and the Xystons, they had far more time on their hands.
With Starkiller being Illum, I image Palpatine has great glee bleeding the planet's crystals.
For the Xystons, it is a Sith World....who knows how many Sith were there over the millennia. Plus a Sith cult and over three decades to do whatever they wanted. Plus I imagine Palpatine could bleed a crystal for a new Star Destroyer just to keep from being bored.
As for the Orange sabers....I wonder if flooding the crystal with a different strong emotion would result in something that isn't quite red. Instead of anger and hatred, what about passion?