The reason you see so much similarity is because this is what works on a practical level and also because people tend to emulate what came before them. Once you get going you will find that most people want looks followed closely by ease of use. They will sacrifice a little for looks but not much.
Anyway, the tubes you can find in the hardware store, electrical tubes for the shafts and plumbing tubes for the butts. Leather suppliers and lots of great advice about how to do anything in leather can be found here
www.leatherworker.net Hardware can be obtained from
www.ohiotravelbag.com among others.
You can also build a case around anything, you can use just leather for the walls, there are tons of ways to do it. It's not rocket science but there is quite a difference between just a container made to hold cues and something built to last a long time that truly protects the cue.
Good luck. There are several new and still unknown case makers I know of who should be coming out with stuff soon. It should be very interesting to see what they come up with.