Be a specialist in a lot of things
You're not a generalist - you're a polymath specialist. Anyone who can learn C# in 2 days, well enough to spot the mistakes, is already good enough to add value to a C# project, and would be a tremendous asset to any IT project.
Obtaining recognition for this ability is just a matter of demonstrating your value to your potential clients.
Before starting my own app business in 2012, I was an IT contractor in London, working the merchant banking circuit. I never had trouble landing the highest paid contracts, despite the fact each role was significantly different to the previous role.
The reason - I never present myself as a generalist, I presented myself as a specialist with a broad range of skills.
When pitching to a client, I work out what they want, and list recent occasions on which I used the skills they require. If I don't have that exact skill, I try to demonstrate the relevance of a similar skill.
When I wanted to move into C++, I was straight up - I said "I don't have a lot of commercial C++ experience, but I've been working hard to learn it. I'm hoping my skills will be useful to you"
Obviously this was a challenge to ask a lot of difficult questions - but I passed.
When interviewing once for Microsoft, they got so desperate to find a question I couldn't answer, they started asking about internal details of SQL Server. I said "come on guys, I haven't seen the sourcecode". I got that contract as well.
Be positive about your approach. Nobody has the exact skills clients need. But you can demonstrate that you will add value to their project, by being confident, by demonstrating your relevant experience, and by demonstrating how you have handled learning new skills in the past.
Eric Worrall (click the link if you want to ask me more questions offline).