NAICS and PSC codes can help you find the most promising customers and understand spending on your products and services.
Using USASpending.gov: USAspending has data on all government spending, so a quick NAICS or PSC search can get you the data you need to size your market. But you’ll need some experience with Excel.
Using FedScout: FedScout has a free built in market sizing tool. The underlying data is the same as USAspending’s but FedScout does the excel work for you.