KR808D-2 is the favorite 2-piece of high-priced rebranders that stick their own name on it. It is not a popular threading other than that.
I know of no place other than China that sells KR808D-2 aka E9
batteries. However, at AzSmokeFree.com you can buy an entire KR808D-2 kit with 2 auto
batteries for $37 - that may be your best bet for batteries.
As for cartos - AZSMokeFree has a very small selection of 18mg. Other than that, the other "name" brands (not Bloog though - Bloog used to be KR808D-2 and now they are the more-supported threading KR808D-1)
These are some of the name brands that sell D2
Smoke 51 Duo, Green Smoke, LeCig D2, Red Dragon, Vapure
As an alternative, I recommend getting out of the KR808D-2 line and buying a KR808D-1 manual battery kit instead (see VaporLeaf.com or LiteCigUSA.net for simple kits, Vapor4Life for colors and prefilled cartos). You can buy D2 to D1 and D1 to D2 adapters at leCig. KR808D-1, not KR808D-2, is the threading supported by the normal price multi-brand market, supported for blank cartomizers of many kinds, and supported for adapters to use atomizers.