You can buy the Aspire CF Mod here (Black only), on sale for $7.49:
Aspire CF Mod
It takes a single 18650 battery (not included).
To use an Aspire K1 tank on the CF Mod, you'd need to get an adapter, since the tank is eGo threaded. But they're cheap at about $1.50 on sale.
The Aspire K1 tank can be bought at many places, as well as the Aspire BVC coils it takes. I have 3 now, after a neighbor recommended them and I got 1, and then ordered 2 more when I found out how much I liked it.
The CF Mod and tank won't be a seamless fit together though, diameter-wise, if that matters to you. The tank is a smaller diameter than the CF Mod is. Of course, a cone used where they attach would make a more clean-looking transition between them.