Confirmed by JDP (who can search Gamebase64 far better than I!) that these were in fact released on the C64 in some shape or form and can be downloaded from here:
http://www.gamebase64.com/game.php?id=5595&d=18&h=0
http://www.gamebase64.com/game.php?id=5414&d=18&h=0
Case closed!
Contributions: JDP, Sean O'Neill, Retrocollector.org
More news regarding these two titles. The Commodore 64 versions of them were also finished and released:
http://www.gamebase64.com/game.php?id=5595&d=18&h=0
http://www.gamebase64.com/game.php?id=5414&d=18&h=0\
They are available for download at Gamebase64. The only game developed by this company (Bignose Software) which so far seems to be missing for the C64 is QA!
Wow, I can’t believe i’ve missed these somehow!! I had honestly checked Gamebase64 for both games at the time of writing, and I had no results come back – which can only suggest that i’m crap! Great news though, and thank you for doing proper research! I will update and close the entry, referring to those two links and add a credit to yourself. Many thanks! :)
The Atari 400/800 version was certainly completed and released:
http://www.atarimania.com/game-atari-400-800-xl-xe-opera-house-qa_13392.html
Thanks JDP! Another case where I haven’t done my homework properly, sorry about that! Added and credited.