>Unfortunately, at this time, it only works with PostgreSQL and every time we show it to PostgreSQL people they love it but want it to be open source. Obviously, we had hoped to sell it so that's a big disappointment.

Just because you make the software open source doesnt mean you cant sell it. At its rawest form open source just means that you are going to share the source code.

If a business is big enough that they have staff who can integrate your open source project would they have been a customer of yours anyway? And if they arent going to be a customer, why not have them as a tester and potential contributor? And if they are a serious company, they usually want a service contract for crucial pieces of software.

You could even have a license that allows using and modifying your software but limits redistribution (i.e. selling) although I wouldnt recommend it.