#1 recommendation from me would be Mojo Tactical on Sand Island -- same building as OGC.
https://2ahawaii.com/index.php?board=24.0#2 would be to try Prime Sports on Nimitz.
https://www.facebook.com/primesportshawaii/https://2ahawaii.com/index.php?board=47.0As far as holsters go, the selection on island is usually limited to the most popular brands & models for the most popular handguns as well as "universal" holsters that fit a variety of pistols in a certain range of models. That's not always the best solution for everyone's particular needs.
Knowing that, you should shop online for what you think are your top choices, then see if you can find it locally. Otherwise, you'll be likely to buy online later, and the locally sold holster will wait in a box to be sold for less than you paid. Don't just buy one locally because it's the only one they had that fit your pistol. Way too many options out there to settle on "whatever's in stock".
As for seeing something in person, Amazon has an excellent refund/exchange policy. They even pay return shipping.
You might also ask on the forum if anyone is heading to the range that has a holster you'd be interested in checking out.
I have several holsters for my pistols, but gravitated to a specific brand and model for OWB. IWB is almost always dependent on the firearm. Holster designs that work well for a smaller pistol might not do as well for a larger, heavier one.
Just trying them on isn't going to give you the full picture IMO. You need to put it on, adjust for comfort and presentation, actually carry a pistol in it (while loaded), and compare how that feels to you for wearing, drawing and reholstering.
Materials used, designs accommodating a mounted light or not, various levels of retention, retention mechanisms used, paddle vs. loop, etc, etc. There are so many things that can influence your satisfaction with a new holster.
Best thing I can advise is stay away from the Blackhawk SERPA style. There are those who like and trust them. If that's you, then I have a few I'll sell you.

Otherwise, make sure whatever you get conforms to recommended AND APPROVED holsters at reputable firearm training schools. I know Front Sight won't let any student use a SERPA.
When I went to FS, I used an Alien Gear OWB/IWB concealment holster that had plenty of retention without any buttons, levers or gizmos to release it. It has plenty of retention for concealed carry, but I use Safariland for Open Carry -- with the thumb lever to unlock it.
Many holsters are expensive. Finding what works for you can take a few tries.
As for training vs. non-training holsters, train with whatever you plan to use in real life. Of course, competition shooting has a whole other set of "rules."
