Ignore what they say publicly about what they need, most companies are (mostly) always open to talk with good developers. If they don't have open positions today, they might just be waiting for a funding round to close, or something else, and you can be first thought of at that point :)

I usually worked for companies building stuff I myself used in some way, or was interested in using their stuff. Companies that organize community events tends to be easier to approach too, if you do it in person at small non-busy events, even better.

Basically, if you see some product/company you'd like to work with, figure out what you could help them with, write them an email and point out exactly what you think could be better, and why you're perfect for them. Worst that can happen is that you spent some hours writing it and they say "No" :)