I'm curious about these as well. I've seen them at Petland (Kahala), Coral Fish Hawaii (Aiea), and Kalihi Pet Center (Kalihi). I see some shrimp at Aquascapes, but I didn't think they sold them, but they did have Opae Ula for sale.
The last time I've been to the stores they only had a few left, or none at all though.
Some have blue-ish colors, some red, some just plain gray-ish. Many in the tanks were dead though...