If you're talking about a double filament bulb that'll fit into the projector housings of the 2G B6/12, I'm not aware of anything that'll fit. You may be able to modify the lights something like Bazza did and use housings that are designed for a double filament bulb.
You may be able to purchase two Hella High beam units. They take H-9 bulbs which are really just high beam bulbs, but I understand that H-9 to
H-11 bulbs are identicle bases. I am thinking one of these may be a dual filiment bulb but I have no idea for sure. (The high beam units fit nicely in the bug eye unit by the way, and when I got into my conversion, I thought about going this route). This is the only way I can think of doing a twin low/high combo. I warn you this is a pretty major job even if you're handy.
You would then have to purchase or build a new harness.
I would give Susqehanna a call to inquire about what dual filiment bulb would fit into the Hella high beam unit. (they are at the top of the page on the link I supplied below.
I went with a low beam/high beam combo, and you would not be accomplishing anything by running a dual filiment bulb in the low beam projector unit they sell, as the beam is projected with these not to blind other drivers. You would need to do this with two of their free form high beam units. I think it would work fine if you could find the right bulbs.
Here is their website:
http://www.rallylights.com/hella/90mm_modules.asp