Why looking for a small one? They can grow pretty big, pretty fast! How big is your tank? I have 3 Haddonis — red, blue, and green. They can get huge so please plan accordingly, even for a 3-4”.
You can try Coral Anonymous - they do have Haddonis.
Btw: if you can find a Gig, let me know? They are like unicorns nowadays.
Good luck!