I also looked for boombox cassette players they are all chinese, Quality products are obsolete now.
Even those 3 or 5 CD changers Mini HI-fi by sony , LG all gone. Now they 're manufacturing these stupid looking portable single unit party speakers and soundbars.
yes, I do own one of these Panasonic SC-UA7 (sounds very good) but when audio is recorded in stereo wtf will these portable boxes do.
My 90s music system worked for almost 16-17 years and I still got many hindi english cassettes, but same like you, these cassettes are all 20+ yr old now. some are even 30+ years.
Cassettes sound more organic, kind or juicier or addictive.
Nothing special we can do for these cassettes, best we can do is to keep playing them and store in dry and cool place avoiding the only enemy (moisture).