At auction:

<LINK_TEXT text="https://www.ebay.com/itm/Monette-Prana- ... 4177541794">https://www.ebay.com/itm/Monette-Prana-BT1-Bass-trombone-mouthpiece/154177541794</LINK_TEXT>

<LINK_TEXT text="https://www.ebay.com/itm/Lightly-used-K ... 4177549806">https://www.ebay.com/itm/Lightly-used-Karl-Hammond-11ML-large-shank-mouthpiece/154177549806</LINK_TEXT>

Also, Stork BT 4.5S LT (pictures available) Light weight version, with symphony backbore (i.e.- chamfered end) $65.00 + shipping