One of my/our side projects is actually basically the same concept (different components), with a similar backstory (except they grew out of contract work - and yeah, I retained copyright), but a little further along. You can actually already trial and buy our components at
http://appuicomponents.com/We've been too busy to actually promote it since launching, but also not really sure how best to go about it. We get a bit of organic search traffic, but it's not enough to make the effort worth it so far.
I actually searched for components like ours before embarking on the projects that needed them, and would have happily paid for them, assuming source code was provided. The iOS platform isn't that stable and I'd be very worried about relying on the developer to update the component(s) fast enough in case of breaking changes. I don't know whether that means there's a sustainable market out there, but I do know some people do make a decent amount of cash with it.
One thing I haven't seen elsewhere are trial versions. We provide an x86-only binary + headers for free, which means it only runs in the Simulator.
