I have been searching for the answer this to this question but cannot find anything definitive.

I like the way gain data is stored for MPC files, i.e. as a separate text file for each album. Is it at all possible to do this with other types of files than MPC, particularly MP3?

I've searched this forum, and tried both foobar and mp3gain, but I can't seem to find a way to do it, or a definite statement that this is not possible.

Could anyone shed some light please?

What software are you using that stores the gain data for MPC files in a separate text file? Are you talking about storing the actual gain data used for the files or just a log of the values calculated?

As far as I know, MPC files store the gain data as part of the file header. (I could be wrong about that or maybe you are using a piece of software I don't know about.) If you just wanted to have a log of the values calculated, you can create that using MP3Gain. Just select Options->Logs... from the menu and you'll see where you can specify different logs to be used for errors, analysis or applied changes.

(I don't know if you can specify a log file that depends on the path or album of the files you are currently working on. If not, I don't think that feature would be too difficult to add.)