I've done the majority of my diving in Maui. For boat diving, my go to's are Mike Severns Diving (
Mike Severns Diving) for the south side (Kihei) and Extended Horizons (
Extended Horizons Scuba Maui) for the northwest side (Lahaina). Based on facebook updates, I *think* Mike Severns is open but I'd call to make sure. I'm not certain about Extended Horizons so you'll need to call, but I would highly recommend them over Lahaina Divers. Lahaina Divers has huge boats with lots of people whereas both Mike Severns and Extended Horizons have smaller boats that max out at around 12 divers - plus the people at both of these operations are top notch. When I dove Lahaina Divers, it was much more hit & miss when it came to guides, etc.
If you can't get boat dives, there are also lots of great shore dives available. I usually stay at Kaanapali (just north of Lahaina) so most of my shore dives are in that area - and they are awesome. In particular Mala Wharf and Black Rock are standouts - both as day and night dives. Mala is probably my favorite - so it's no wonder it's also a common boat dive location from many of the local dive shops. Amazing dive and it's only a few seconds drive to the dock. If you shore dive it, try to do it at high tide as it makes the walk out far easier.