I'm sure people would love to trade back and forth to keep blood unrelated. You might want contact Julirs about it- I know she is working with pygs.
As far as WC VS CB, CB pygs do pop up occasionally, but I think at this point it will be difficult for you to rule out WC animals entirely. They are a little more difficult, but I know that FLchams does really well acclimating them before sending them out. There just aren't a ton of CB pygs around, and what there is may be related.