Not what you're asking for, but for what it's worth:
I just traded a Clem H for a Susie Longbolts, moving my 58cm "normal" bosco moose bar from the former to the later. When I had the Clem, I too searched for one of the rare, down-sloping Bosco bars, because I thought I'd prefer it. (Prior to the bull moose version, I had a normal, separate bosco and did angle it more downward by quite a bit.) However, on the Susie I feel content with the angle of the bars on the "normal" bull moose version. The head tube angle is just enough slacker as to add some helpful slope. And this is DESPITE the fact that the headtube/bars are higher than I'd prefer on the susie. I no longer feel like my hands want to slide forward wnen going down a steep hill.
So I'd suggest trying a normal one if you can even find it. I'm not entirely sure the bullmoose bars - of any shape or angle - will be easy to come by in the future.