As have I.
In fact, I've also seen not only factory parts with both a CD and cassette in the same unit, but aftermarket ones as well.
But, they're pretty expensive, too.
I'm kind of in the same boat. I had my current car ('94 Bonneville) for a short time, when fate decided to put me in a Pontiac dealer swinging wrenches for a while.
While there, I made a bit of a side deal with the used car manager there, and swapped out my factory radio w/ cassette, for one out of a auction bound car with a good working factory CD player. Straight swap.
But now, I too have boxes full of cassettes I haven't been able to use (in the car, at least) in a few years now...
I'm kinda surprised some enterprising fellow hasn't designed a unit to fit in a CD-ROM bay of your PC, that plays cassettes. Not a whole radio (although they could certainly build that in too), just a tape deck. Kraco (among others) used to build these little under-the-dash add on units twenty years ago so you could play cassettes on the old AM/FM car radios. These were smaller in size than a PC optical drive is.... They ran on 12V, just like a PC uses.
Heck...make a PC 8-Track player too...for us real old fogies.