XT2s and XT25s are available LH new from Thomann. Don't forget the prices they list incl 19% VAT which you don't need to pay. Shipping is about $A200. New or used LH units are very rare.
Make a strap pin extender, a 1/2 hr $10 job to make it hang correctly. The pickups are OK, but guitar HBs fit and many sound excellent like the Wilde L90 and L500 work well in this application. Several builders on TB have used them. 7 string guitar HBs fit the 25s. Tone is personal and I've used the woodbergers live, not perfect, but good enough.
They are 98cm long unbagged and are less bulky than a trombone case and other bag for a neck off bass will be. I've travelled with my XL2 and woodbergers a lot. Just beware that shotgun bags, which are cheap and fit perfectly and are well padded can bring some looks in airports, but my guitarist has travelled with my Spirit guitar a lot internationally with no issues in the factory bag.
If you intend to use a conventional bass neck off, you'd probably be best to add inserts into the neck to facilitate regular on/off cycles similar to Klos with their CF acoustic guitars to save stripping out the neck.
Streamlines and Synapses are expensive now, especially the former, so an XT2 will be much cheaper.