Hello bord - You are correct that "Isabel's Return" did not make the Bremner CD; in fact, I believe the liner notes mention this omission. One must assume it wasn't a substantial enough cue to warrant inclusion. Personally, I thought the scene would play better with music, so for my reconstruction I reused the later cue that plays when George learns of his mother's death from Fanny. I'm fairly certain the "Isabel's Return" cue was cut from the film because it bridged the carriage ride into the hallway scene in the original edit. When the hallway scene was deleted (along with a few seconds of the carriage ride), the cue probably no longer worked (Check Page 2 in the "Welles And New Digital Technologies" thread for more info on how I utilized the Bremner recording).
There are quite a few "Ambersons" stills available in the Lilly Library collection in Bloomington, IN, many of which show up in the Carringer and Bogdanovich books. Some are actual frame enlargements from the cut footage...although, unfortunately, it seems that some of these may have disappeared or been misplaced over time. Joseph McBride has mentioned seeing a frame enlargement of the final matte shot of the dark, looming city as Eugene's car pulls away from the boarding house; this was in 1970 when Bogdanovich had possession of supposedly 70 - 100 such stills. According to McBride, Bogdanovich claims to have turned over all of those photos to Oja Kodar who may still have them in a box somewhere in her Croatian home!