The only ones I've seen recently are being sold as part of a complete tubeset at $1,000 or more. I think you'll be very lucky to find one available by itself, and even then it'll be pricey.
If you've already got the tubeset, you might just use a generic BB shell and either fillet braze or TIG weld the tubes to it.
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- Stan
my bikes
Science doesn't care what you believe.