If you have trouble locating any of these papers please contact an author for a reprint. A few of the later G.P. Srivastava Group papers are available as on line Postscript documents.
G P Srivastava and G S Verma
Phys Lett 41A, 61- (1972).
G P Srivastava and G S Verma
Ind J Pure and Appl Phys 10, 750- (1972).
G P Srivastava, D P Singh and G S Verma
Phys Rev B 6, 3053-3055 (1972).