How about some daxophone, from Hans Reichel?
I have one of his discs very interesting. This one is a bit jazzy but definitely it’s own sound.
Lubomyr Melnyk made some interesting pieces although his newer material is more new age. Continuous music theory and many notes.
Harry Partch and New Band also did quite a bit of instrument invention and also there is this guy who made some fun stuff.
Then there is the nightmare machine very cool.
An interesting electronic sound world from 1975
Bernard Parmegiani- De Natura Sonorum
And fall into the musique concrete with Luc Ferrari
thanks for the links.