Local fish stores will sell bigger Corals, just charge you more. Best bet is local reef clubs. Many times people have to trim big colonies and will sell frags of common Corals cheap.
Diver's Den (Live Aquaria) will have colonies. Not cheap and they don't do the best job photographing them.
Also be aware these are almost always wild colonies and success rates are substantially less than frags that come from a colony that is already thriving in captivity.
Local club guys sell frags. Before they are fragged, they are big. Just contact them and ask if they have something thats not been fragged yet. Big colonies like red dragon go for around $500