One of the first places to check are the larger for sale or trade sites (FSOT). The Babywearer has a free FSOT area but requires you register for the group.
If you are a patient person, another option is to buy a carrier on a pre-order. In this case, you are buying before the carrier is made.
It is a good idea to “Like” the facebook pages of your favorite brands. Some brands also have a newsletter. Many manufactures will post when they are stocking new carriers and when new options are available. Then, it is just a matter of being patient and hoping for a good computer connection when they stock.
Finally, if you are truly obsessing with a carrier and don’t want to inadvertently miss one of their postings, you can sign up for hyper alerts. Hyper alerts are free and will send you emails when updates are made to Facebook pages. Since you can’t control what shows up in your facebook feed, this is a surefire way to know when your favorite brands are posting.
Happy searching and best of luck.