Currently, there are no wooden tunnels for either animals. Plastic tunnels are essentially much more readily available and are less likely to cause a fire.
You can find wooden tunnels in almost any pet store, although I believe they are less common than plastic ones. Many woods are not safe for hamsters and gerbils.
I never seen any, but they are very easy to make. You just must make sure that the wood was never treated and that it never was used around pollutants.
Why would you want a wooden tunnel? The fun of the tubes is seeing them run through the tubes. I'm sure they don't want to do this in the dark, it wouldn't be fun for you or them. I'm sure there is someone marketing wooden tunnels.
Yes. Although plastic tunnels are much more common and easier to find, a google search will reveal a number of sites that sell small wooden tunnels. Of course, I still prefer the toilet roll tunnels personally *smile*.