Code:
> buy 6 rad lib
Searching for "Rad Lib"...
Search complete.
Purchasing Rad Lib (6 @ 1,200)...
Purchasing Rad Lib (6 @ 1,200)...
Purchasing Rad Lib (2 @ 1,380)...
Purchasing Rad Lib (4 @ 1,390)...
Desired purchase quantity not reached (wanted 6, got 0)
> acquire 6 rad lib
You need 6 more Rad Lib to continue.
> inv rad lib
Tome of Rad Libs (18)
If I had to guess, explicitly adding the plural to Mafia ("Rad Libs") would fix this.