Not exactly what you're after and you might have it already, but I have:
Investigation of Tail Buffeting Conditions on Lockheed P.38 Airplane
including Appendix I - Investigation of Dive Characteristics of the YP-38 Airplane
Lockheed Aircraft Corporation Report No. 2414 February 1942
and
R.A.E. Comments on Reports of Flight Trials of Lockheed P.38 aircraft. (5638 - Ae. 1931)
March 1942