Good luck with that. To my knowledge, the BT1100 was designed specifically to fit the L48 and nothing else so the chances of finding an orphan BT1100 must be very slim.
Not much showing up on Google... here's one in Canada from last year, I think: Kubota BT1100 L48 Backhoe Attachment For Sale | AgDealer.com
You might try some tractor or construction equipment salvage yards. You might get lucky and find a scrapped L48 with a hoe that could be rescued.