The K1 is an eGo-sized clearomizer, right?
There are larger options in the Aspire product line that have BVC heads available, one being the Nautilus and another is the vivi nova-style of the regular Aspire tanks (both are around 5ml capacity if I remember right)
I think the K1 uses the same heads as the original Aspire tanks, but I'm not 100% sure on that. The Nautilus, however, uses a different coil head so any you have on hand now won't fit that one