There is an Australian Blu Ray called “Wallace & Gromit: The Collection” released by ABC in 2016 that is 1080/50i. It has the same music alterations as other BD/DVD releases but is the highest quality with the correct speed/pitch.
http://www.blu-ray.com/movies/Wallace-and-Gromit-The-Collection-Blu-ray/160598/
I also managed to grab a TVrip of The Wrong Trousers from UseNet which was recorded from BBC One around Christmas 2007 which has the original audio. One problem with this one though is that it has a voice-over/announcer at the end credits. I don’t have any means of ripping my AUS BD but if anyone wants me to share my BBC TVrip, I’d be happy to upload it somewhere.
I was thinking these two sources could be muxed together without any need to re-pitch anything and create the highest quality version.