Based on what Cheesehawk wrote I found some of the skins I wanted at
http://cliffsofdover.fr/ , and as I look at them I can see it looks pretty easy to use Photoshop or Gimp to add the hakenkreuz into a default skin, if I can't find a skin for some of the German planes.
A big part of what prompted me to start this thread was warnings such as this at other forums where skins are shared:
"***VERY IMPORTANT***
This skin is NOT for use online and WILL get you BANNED if you use it online. DO NOT USE WHILST ON MULTIPLAYER OR WHILST YOU ARE ON STEAM AS YOU WILL POSSIBLY GET BANNED
If you do want to use this skin we recommend disconnecting your internet connection and then using it, and if you do want to go online with the game please DELETE the skin before you proceed (just as precaution but HIGHLY RECOMMENDED)"
But I eventually saw a post explaining the above is that skinner's best attempt at a full disclaimer to address all
possible consequences of using anything but the default skins, and is not based on the consequences we
know will happen.
So, I'm probably going to take the risk of flying off-line SP with historically-correct skins while still connected through Steam, and I'll do what Blackdog recommended and check my VAC standing.
As far as online MP flying goes, in addition to possibly running afoul of a VAC ban, Ataros gives a valid enough reason for me to fly online with only the default skins - I don't want to create any stutters for other onliners.
I'll just need to keep back-up copies of the default skins folders so I can quickly swap them in when I venture into online MP servers.
Many thanks for the helpful advice, everyone above!
Charlo