Re: Mini circuit board needs replacing
The PCB is/was part of the onboard distortion circuit of the OP's Yamaha Super Flighter guitar.
The part is no longer in production. It ought to be possible to etch your own direct replacement board or create a near equivalent using Veroboard.
In my opinion, unless the onboard distortion was producing sounds that are absolutely essential to your music making, the smart option is to reconfigure the control circuit to something more conventional. e.g. 2 Vol., 2 Tone or M. Vol., active tone controls or boosters.