1. Take your closest circle of friends and family. Cross off anyone who is also a developer. Among the rest, look at people who are professionals or small business owners. Take them to lunch. Ask if you can shadow them at work a bit. Take copious notes. Find out what the most annoying/tedious part of their business is. Also, if they rely on clerical/support staff, talk to those people too.
2. Pick an industry that you have an interest or curiosity in. Put a job posting in your local Craigslist for people in this industry (ex: mortgage brokers or elementary school teachers). Say you are looking for an advisor to discuss some startup ideas. You will get several responses. Have lunch with a couple people. You don't have to have ideas up front. Just ask them the same questions as option 1 above. Ask them if they'd be willing to beta test something you built.
Protip: there are some industries I'd suggest avoiding. For example, restaurant owners are extremely busy and working in a very low-margin industry. They generally don't have time to meet or test things.
Disclaimer: these are mainly B2B strategies. Most B2B problems really boil down to saving money, making more money, or saving time (time is money). If you can do any of those things for someone, they will pay you.