Immediately voodoo comes to mind, I know they have a Ti 29er offering that has sliding dropouts, they are also slated to start production on a 29er bokor which if they follow their normal recipe it should have sliding dropouts as well.
Here are some other options that come to mind quickly:
I do also know of another company who does work with steel frames that is in the beta phases of their own 29ers with sliding dropouts that I would expect to start becoming available in short order. I don't think they have announced it yet so I won't mention specifics. If you can hang tight I would expect more and more companies to incorporate a similar tensioning style or at least most coming with EBB's
nicknamed "paragon sliders".
LOADS of companies do them, any custom maker, and kona, voodoos, specialized has a version of them (or did?) several companies are now moving to swinging dropouts ("black cat" style)
The Ti frame pictures is a Lynskey. The sliding dropouts are called "Paragon Dropouts", because they are manufactured and distributed by Paragon Machine Works (with all due respect to Ground Up designs . . . .). Kona, for one, has a sliding dropout, but it is not a Paragon dropout.
Cheaper than ti handmade in steel are the Siren John Henry, Curtlo, Misfit Cycles FE, and Curtlo. For a little bit more but still less than Ti is a Waltworks. Prices start to go up from there with custom frames, but like mentioned above, almost any custom builder can build you a frame with the paragon dropouts.
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