I've recently seen praise for the XO Bass Trombone. I have no independent knowledge, but just stumbled across this listing on eBay:

<LINK_TEXT text="https://www.ebay.com/itm/Jupiter-JSL-12 ... Sw3tdeOdRY">https://www.ebay.com/itm/Jupiter-JSL-1242-XO-Series-Double-Rotor-Bass-Trombone-Bb-F-Eb-D/254579908252?hash=item3b46251e9c:g:QK4AAOSw3tdeOdRY</LINK_TEXT>