You really only have two choices.
First choice -
1: Purchase all available instrumental versions.
These come in various shapes and sizes. Karaoke Queen, Queen The eYe, The Freddie Mercury Collecion, CD single B-sides, 12" singles etc.
You may have to do a little homework first - but there are a lot more available than you may think.
Second choice -
1: Purchase all available 5.1 versions. (DVD-A or DVD-Video).
2: Isolate each seperate track.
3: Use each separate track as either:
a: A stand alone mono track.
or
b: Part of a combination of multiple tracks used to permatate a new "series" of "mixes".
You could always cheat and make your own (certainly people like Dark seem to rave about things like MIDI files), but you will notice that I have not included this as a "real" choice - simply because it is not the real McCoy (or Queen even!).
Other than that, I am with BHM1775: "Erm ..... No, they don't exist".
In that case, wouldn't it be better to get someone who plays bass and another for keyboards?
If not, editing some midi tracks to your liking should be pretty simple work.
Peace,
Adam.