The Robert Wood Johnson Foundation has a publicly available data source you can use to find this information. Known as HIX Compare, the data contain descriptions of plans in the individual and small group markets across all 50 states.
HIX Compare is the only dataset with information on nearly every individual and small group marketplace plan offered from 2014-2018, and most off marketplace plans as well. HIX Compare contains information on plan characteristics, such as premiums and benefit design. HIX Compare is a machine readable file available in CSV and Stata formats.
Here is the HIX Compare data documentation. The data have been used for a variety of purposes including measuring the effect of risk corridor programs on premiums, the presence of narrow networks, and many other studies.