She came in the original Dark starter, right? How can I get the model these days?

I would suggest looking for online retailers or FLGS in your area for the old starter. Dark Cheshire is in both the old and new Dark Starter set, so you're gonna get him no matter what. I'd suggest buying the old set, and then buying Bael as a separate figure. (She's really an awesome sculpt). I'm sure that Shinigami will be available as a single figure in the future, but I'm not sure if anyone knows when.

Shinigami Ayl will be available as a blister in January/February.