Don't be afraid to contact any of the Bamboo makers, they can and often will build a blank to whatever specs you want. H&H a sponsor here has blanks. There are some decisions you must make, ie... do you want to ferrule your own blank or have the maker do it for you.

Another thing to consider, there are a number of makers that offer classes to take a culm all the way to a fishing rod. There's nothing like fishing your own grass!

most of all enjoy the obsession.