Ask HN: Where can I find Mac beta users for our software?

Politely contact @dahowlett and talk to him. www.accmanpro.com. Former Chartered Accountant. He knows stuff and will not BS you. Read his Twitter stream first. Read his blog first. Go back as far as you can in your research. He does not suffer fools or lazy people.

Check out http://macdeveloper.net/

You offer a incentive to testers there and they give you feedback on you app. I've used it a couple of times with really good results.

Buy adspace on Daring Fireball, and try the Fusion ad network too if you're looking for Mac users (since in my (relatively anecdotal) opinion they do reach a lot of Mac people), also The Deck.

I'd try the Apple subreddit (http://www.reddit.com/r/apple).

I'll try.