Some of these are hopefully currently available, others obtainable.
Breitkopf & Hartel published a book of pieces by Schobert- chamber works,
concerti, etc.- in 1958.  Sibley Library at Eastman School Rochester
has this.  There is a 1992 publication by the publisher J. M. Fuzeau,
in Courlay, France, of his sonates en quatuor op. 7.  J. P. Hinnenthal
Verlag, in Kassel, published the opp. 9 & 10 in 1960.  (Notes that there
is or was also a recording of Schobert on ASV, CD GAU 172, of the sonatas
opp. 5 & 6, and another of op. 16 on GAU 156.) Hope this is at least a
start.

Eric Schissel