Below are a few trade sites and organizations that provide useful information on the outdoor industry. I will add to the list as I discover additional useful links.
IbisWorld is a great resource to get a broad understanding of large industries within the United States.
Use this as an introduction to industries to become more familiar with what’s happening in your prospective industry.
Because the reports are so specific, you won't find anything for "outdoor industry," but rather reports for hunting, fishing, hiking stores, parks, etc. which you can use to understand the broader outdoor industry.
First Research is a nice compliment to IbisWorld and will also cover broad industries.
Use First Research to get a different perspective on the industry than IbisWorld offers.
Suggested reports include "Recreational and Vacation Camps," "Recreatonal Vehicle Parks / Dealers," "Boat Dealers," etc.