Plea for a lost recording MAYC London Weekend late 1970s

I played in a band called “Spectra” performing at the Festival Hall I think (definitely not RAH – I was in the orchestra for that one) in the late 70s.
I always meant to get a copy of the recording that was made but I never quite got round to it and now I would really like to hear it. If anybody knows where a recording might be available I would be really grateful. If it helps to narrow us down we were a 5 piece band with a female lead singer and I remember we opened with “Roll over Beethoven” and finished with “Really amazing grace”.
Thank you 🙂