I've sometimes been invited to these events, especially those held at department stores or boutiques. I've also taken part in fashion events held at event venues.
I was at Petite Fashionista Presents most recently and found a beautiful dress. It's the berry and black one in the fashion show (in the 30 second point) segment seen in the video below
These events, especially those at event venues are great if you're looking for designers that you might not find in boutiques. However, there's often limited sizing and product. They only had one dress in my size, for example (actually two. The other one was worn by the model)