This is not a guide on how to plan a wedding, but rather on how to find information on the business of weddings.
The "wedding industry" is large industry in terms of dollars, but tracking where that money is spent is more difficult for several reasons.
This is an industry that is made up of multiple smaller enterprises that are part of different industries like caterers, wedding consultants, dresses, various beauty suppliers (hair, makeup), photographers, favors/bridesmaids gifts, music, honeymoon related, etc. While the industry as a whole represents a lot of money, each of the component parts is much smaller -- some smaller than others. These smaller composite suppliers can be very local and likely will be small and privately owned -- traditionally the types of businesses that do not necessarily report financial information to any agency other than the IRS. This is in sharp contrast to larger industries, comprised on many public companies which are required to file with the SEC making it much easier to find information. These larger industries also affect the economy as a whole on a much more obvious scale, also making it easier to find out information on them.
Since overall industry numbers are going to be hard to come by, other ways of finding the information will be necessary. One way is by searching local (and community) newspapers,which may provide information on a local market. Also, there may be individual accounts of weddings that would be relevant. Contacting local companies/people will provide someone with experience and knowledge on the local scene. Try the local phone books under weddings, party planning, catering, event planning, etc. to find the local companies/professionals. Also, ReferenceUSA (often available in local public libraries) is an electronic directory with SIC/NAICS codes search limitable by various geographic search functions.