The Australian Standard, AS4100 "Steel structures", deals with lateral torsional buckling of monosymmetric I-sections. AS4100 references the following paper, which may be of interest:
Kitipornchai, S. and Trahair, N.S.,
Buckling Properties of Monosymmetric I-Beams,
Jounal of the Structural Division, ASCE,
Vol. 106, No. ST5, May 1980, pp941-957