TUI uses Freebird for some years now on their weekly Turkey flights from at least BRS EXT BOH and NWI iirc, and as they have 9 MAX a/c out of the fleet as you know they are subbing in
many carriers such as Olympus A321 and ASL France 738.
TCK has several Smartlynx aircraft on lease all summer based at a few airports (BRS is one)
The guys in the TUI Jet2 and Thomas Cook airline pages seem to know how the leases are going - suggest you post there?
The Balkan Holidays BRS-Bourgas flight has seen MD-82's and 737-400's recently
Norwegian at LGW are subbing all summer (due 787 problems) Wamos A330 HI-fly A340 Privilege Style 777 and Evelop A330 on their MIA MCO ORD DEN and one of the JFK flights - all of which are on flash sale fares right now.