There is an option in the game that allows you to turn auto downloading off. If you select this you can download selected skins from HTC's website. Limiting the number of skins you load can reduce or stop the stutters you get when the game has to access the HDD for a skin not in memory.
There are no skins for the F6F, N1K Il-2 or 262 because those plane shapes were changed in the last version. I've submitted some F6F skins and I believe Busa has submitted some N1K skins for the next skins update.
Possibly one or more of the P-38J skins was moved out of the rotation sequence. Only 15 player skins are allowed per plane and the 38J may be oversubscribed.
For non subscribers the only way to view skins offline would be to download some from this site:
http://www.ah-skins.com/However not all the skins here are up to date. Many of them are for the old shape aircraft.