first of all, take all the live sand you want.
Actually you are only legally allowed to collect one gallon per person per day.
as for corals, you can collect all the SOFT corals you want. good places to find softies such as zooanthids and anthelia are sandies, and pretty much anywhere on the east side of oahu.
Zoanthids are not soft corals, also though you can collect soft corals there are only two types in Hawaii, Anthellia/Sansibia and Sinularia ... however, you can NOT collect the rock they are attached to so you have to peel it off not an easy task when it comes to Anthellia. Given the low diversity of corals in Hawaii any reef tank you create will not come close to what you can do on the mainland with imported corals.
It is unfortunate that live rock is illegal to collect in Hawaii, but seeing as most people have no idea of the proper and ethical way to collect it, its probably a good thing.
I am looking into the possibility of legally importing aquacultured live rock
It is not the rock that is the concern, it is the attached organisms such as bacteria and algae that is ... therefore aquacultured live rock from outside the state is most likely illegal. Check with DLNR, Aquatic Resources.
Try
www.ipsf.com for aquacultured live rock from the Big Island.
If you make your own live rock you could most likely seed it and develop it in your tank by doing frequent changes with natural seawater over about 6 months or more. You can NOT just place it in the ocean ... thats called dumping ... you need a permit/lease to do that.
Before you do ANYTHING I would suggest that you contact the Aquatic Resources division of the Dept. of Land and Natural Resources and find out exactly what is and is not legal.
Aloha!
JCD