All of the BTZS products are marketed by the view camera store. You can get the tubes, the hood and the expo developer programs from Fred Newman. If you have questions about the BTZS method you can go to the BTZS web site and get an answer straight from Phil. Here are the links.

http://www.viewcamerastore.com

and for the BTZS questions:

http://www.BTZS.org