There's the CMK set #F72115 (US Navy pilots WW2) and the old Airfix/Heller USAAF personnel (in OO scale but could feasibly be used and/or modified as required). The latter may only be available via HaT these days, but search around and you should not have too much trouble finding it.
I seem to recall that Preiser had a set of USAAF mechanics too (check Roll Models), but if not, their Luftwaffe mechanics set may be able to be modified to represent US personnel.
You might even be able to modify/adapt some US infantry or marines figures; have a look here for some ideas:
http://www.plasticsoldierreview.com/PeriodList.aspx?period=1#USA-Infantry/Marines