Invisalign $1000 off discount happen often?

I have been considering invisalign and am ready to pull the trigger. Back in December, I saw a limited time $1000 off promotion that the orthodontists have told me came directly from invisalign. My question is how often does this promotion occur and is there something I can do to get it? I've tried contacting invisalign and joining their mailing list, but so far, nothing.