Dubro also has 6" wheels, $28/pair. These are a bit "balloon like".

Still Dubro, less balloon looking. $19/each

Robart also makes 6" wheels, but these may be out because of the price. They are all roughly $100/each wheel.

I have the Robart spoked wheels on my Top Flight P-51 and I can tell you that they are a true work of art. But they are pricey indeed.

Hope this helps you out.

Ken