So getting the information you need is going to be difficult. Probably the better place to start is by asking former manufacturers. They would probably give you the better feeling for the market. But don't expect it to be upbeat. From there, I'd start asking other questions.
Most folks know that paper tubes are cheap.
Maybe that is the reason that it is so attractive to be a manufacturer. Maybe, you think, there are other rocketry products you can create and sell besides kits. Then you need to decide how much inventory you need to purchase to make it work. If you buy in bulk, you can get good prices. But if you don't sell it quick enough, you have a lot of money tied up in inventory.