[onion2k]

If you're in the position to be selling code to people then (presumably) you believe your code is good enough for people to buy. As such the examples need to be code. If you haven't got examples then you're going to have a tough time persuading people that you're capable of fulfilling their requests.

This is the same problem people have when they apply for development jobs. The solution is to write some code you can show people. Get a side project, or do some work for free (or cheap enough that people will pay even without seeing examples of previous work), or ask people you've worked for previously for permission to use what you wrote as examples of what you can do. Don't just say "I haven't got anything." That won't work.