Data from public opinion surveys, available from 1930-on. Membership-based but some data is free. Search for MARKETING and limit to the years you are interested in to find data.
Quarterly reports that include a specific section on e-commerce retail and online businesses.
Trade Shows & Conferences
Trade shows bring businesses from the same industry together and are great places to make connections with other entrepreneurs and vendors. They are an opportunity to exhibit company products and services.