These showed up on Yahoo Auctions Japan. I wasn't going to bother bidding on them with buying my first replacement months ago but after a week or so went past I noticed nobody had placed a bid. The seller had 5 panels in total and I think I got the two best on offer.
It's very rare to see Q25 spares for sale never mind a unused panel! I've now fitted the 2L12B to my cabinet and it's finished it off nicely. The SSFII special edition 1L6B control panel is going to need a good clean up/new stick and buttons.
It is my understanding that Capcom operated the Q-GrandAm 25 as a rental only machine in Japan. So I'm guessing when Capcom supplied the cabinets to arcades they also supplied operators with different control panels which would allow them to use different configurations. I'm yet to see a 3 player version panel apart from the one in the BGS-25/Q25 brochure which is the concept version.
I've also done a little more work on the paneling to the front of the machine to get rid of any yellowing which has now been completed. Here's a picture of the cabinet now fitted with the NOS 2L12B control panel.