The way I higher anyone is to find people who already do amazing work, approach them for advice on my projects, see if their a fit for our team and skills - then over time (as I work on a project with them) convince them that our company is the best opportunity they have.

So, back to your questions - where do I find high quality UX designers? We'll, here's a few places I look:
- www.dribbble.com
- http://www.behance.net/
- http://www.deviantart.com/
- http://carbonmade.com/

I also like searching on Twitter for bio's with UX design and high influence score, or follower count Ex: https://followerwonk.com/bio/?q=UX%20designer&s=social_authority

If you follow this approach for sourcing great candidates, and my recommendation above re: get advice/start a conversation - then work on a simple project first to see if there's a fit, you should find some success.

It takes time, but the right person can 10x your growth .. so slow down and do it right.

P.S. I also did this once, and ended up higher 2 AMAZING guys!
http://www.danmartell.com/why-i-would-pay-100000-for-an-amazing-ui-designer/