I agree, it takes time.
It's also the case that no matter what niche you're in, there seems to be a given number of webmasters that are going to look down on your work and refuse to link or collaborate.
The good news is that there's typically far more folks out there that are open minded and interested in linking. As with anything involving marketing, at the end of the day it's a numbers game.
For me, I've figured out that for every 10 or so link request emails I send out, I'll probably get 1 success.
Knowing that gives me two choices:
1. Tweak and experiment with the message in my link request emails to see if I can go improve on 1/10.
2. Send out more link request emails.
Of course the key is to do both.
Perseverance and patience are the keys to success.