My guild holds one once a year and it is announced and promoted at guild. Also some small bees associated with the guild will let people know they are going on a retreat if they need more people to book the location.
Sometimes I see something when I am reading blog or otherwise from a quilting teacher that they are teaching at such and such retreat.
I used to think it wasn't worth it because (before becoming a foster mom) I could sew anytime I was off work but the couple I did go to I really accomplished a lot and had fun.