Some options. I included links I had bookmarked.
It's a 45min. drive to Lahaina so the only reason to do that is to dive Lana'i (the Cathedrals) since the Kihei boats don't generally go there. if so Extended Horizons or Hawaiian Rafting Adventures are smaller options. One I don't know much about is Maui Pacific Divers - looks like a small boat (photo gallery) so probably a limited load as well. West Lana'i is typically the fastest drift diving - Lahaina sells a trip just for that. So don't do any of those dives - it can really be ripping - I know firsthand...
Maui Scuba Diving 808 667 0611 Scuba Dive Lanai Extended Horizons - Maui's Leading Green Dive Shop - Lahaina, Hawaii
Scuba Lanai - Lanai Dive Trips, Lahaina Dive Shop, Scuba Lessons | Hawaiian Rafting Adventures
Maui Scuba Diving | Scuba Diving Tours | Maui Pacific Divers
I used Maui Pacific Divers in October. They are an excellent choice in my option. They have a newer boat that takes out I believe 8 divers max. We dove with them 4 days at various sites around Lana'i and also a trip over to Molinkini crater backwall. They also have the best surface interval snacks I've seen on a boat...... brownies, fruit, gateraide, water, etc and have a very personable crew.