Qobuz, Tidal, or second-hand CD purchases (then ripped to FLAC using Exact Audio Copy or similar).
The 1991 edition was digitally remastered from original master tapes by Paul A. Rothchild (the band's original producer) and Bruce Botnick (their sound engineer). FLAC Audio Quality: FLAC (Free Lossless Audio Codec) The Doors - In Concert -1991- FLAC