I bought a similarly asymmetric BB with a Ti axle on eBay in the past. I think it was the World Class brand, and the seller did not declare it asymmetric. I noticed the asymmetry when browsing my stock for something that would fit Brompton, and it was a perfect fit. Moving a symmetric BB by 3mm or so to the drive side with spacers may be possible.

As for tensioner wheels, I made some with bearings useful by pouring superglue into and around the bearings and seizing them.