Don't know where you've tried, but these might help:
AirlineDecals.com
Vintage Flyer Decals Home Page
Authentic screen printed decals for airliner models | Airlinerdecals
8aDecs.::.Aviation Decals
I used Twosix Decals on my Eastern Airlines Lockheed L-1011, and they were quite nice (ok, so the photography isn't that great):