We have 2 of these signs in my neighborhood with hopefully more to come. You can get these where I live (in Ocean County NJ) by a phone call to the local police department, traffic safety. Where I live, there is no charge for the signs.
Update 8/14/08: I returned home today to find that they had put up our new sign! We live on a corner and just a block or so in from a busy street. Though there are 2-way stop signs, I requested one more sign to be put up as you pull in from the busy road. Here's our new sign!