This Module is currently available.
Filters and Attenuator
The C991 module contains two passive filters, a 6 dB low pass and a 6 dB high pass switcheable in 6 positions each. There also is an attenuator. The module is entirely passive and requires no power.
Fender 991103921$327.93
Fender 991613921$327.93
Fender 991713921$267.74
Fender 991103921$267.74
Fender 991713921$314.99
These merchants probably sell this module. Huh?
Yanagisawa Model 991 Professional Alto