Do you have access to clones? If so, there are a lot of purple strains you can aquire, purple erkel hybrids are pretty popular, such as granddaddy purple, Querkle, Grape Ape, uhh too many to recall from reading or hearing about. Blueberry, and blueberry hybrids can have blue hues here and there, and a blueish appearance , but not always, but if you do find some, it's very pretty.
As for ordering seeds online, if you don't have access to clones like a lot of us, I would recommend going to attitude, or hemp depot and just look around at different strains.