I don't know of any third-party equivalent to the B 5 D windscreen specifically, if that's really what you're looking for (with the "D" on the end--the version that was invented for "The Three Tenors"). Most people use the simpler, less expensive model B 5 for most applications--and there are plenty of knockoff versions of that, at least in structure and appearance. I don't know how closely the characteristics of the foam material in the various third-party versions resembles what Schoeps uses, though, so I don't know whether the treble losses are as low as they would be with the genuine item. I have definitely seen some cheap knockoffs use a type of foam that would choke the high frequencies pretty noticeably.
To me it seems a little odd to use expensive, high-end microphones but then compromise their recording quality with windscreens that save you only maybe 1% of what those microphones cost you.