Craigslist: all those shitty no pay jobs in the gigs section. That is for you.
They want an expert kernel programmer willing to work for $10 an hour? Great! You're an expert and you know the kernel inside out.
Those idea guys where you get 50% and no pay? Perfect, talk to those guys, they will give you all the experience you need.
Once you have a few of those under your belt and some sample code, go show the guys looking for pros.
Alternatively, you can go to the LKML or Google Chrome or Firefox dev sites. Download the source, work on documentation, find some simple bugs to fix, etc. Pretty much any open source project would love contributors, go contribute., worst comes to worst they reject your patch, but keep submitting til the quality is up to par.
Basically, just go do it. Whatever you want to learn, just start doing it. It sounds like you're trying to give yourself a list of reasons why you can't do it.
If your looking to transition from a field where you have years of experience to a field where you have little and expecting to bump your salary all in one go I have to say it's pretty unlikely that's going to happen. However, if you're willing to put in time and effort you will have no problem transitioning over a period of time.
The simple facts are that it takes 10 years of programming to have 10 years of experience programming. I spent 5 years doing PHP / C#. Another 5 years writing C# / Perl.
When I wanted to transition to iOS coding I bought a dev license installed XCode and started coding an app for myself and put it in the app store (it took about 1 to 2 months). I've made $30 bux on that app, but the point was not to retire from the app store but to learn iOS. Whatever you want to do, just start doing it, and see it through to the fruition that people are looking for. (eg. on iOS store all anybody cares about is that you've gotten it into the store).
If you're getting paid anything to learn to code you're 10,000 times further ahead of everyone else who are paying lots of money to learn theory, rather than practice. (eg. How many iOS courses actually result in people putting an app in the store?)