The pictures that I've seen of Nuummite (which I haven't met in person yet) seem to show a stone that has sparkly inclusions. If it looks like what I think it looks like, you're more likely to find polished stones than rough ones, because that's going to really help to "bring out" those inclusions and help them sparkle all the more.

Rough Moldavite shouldn't be too hard to come by, however. Just be sure that the dealer is reputable. And compare the size and weight of stones on their site with the prices of stones on other, known-as-reputable sites. Then you'll have an idea if you're paying a fair price.

My one other hint is to look first at dealers whose target customers seem to be rock and mineral collectors. They seem to have more reasonable prices, in my experience. And there are some (some, not all) New-Age-oriented sites that really seem to attach a significant markup to their prices.

If you see a site that insists on adding elaborate backstories to their stones, in order to jack up prices, give that seller a miss. Doubly so if it's a backstory that's really not verifiable by any third party ("My neighbor's sister's guru had a mystical vision and spirits from the Nematodes told him about these stones... they're from meteorites that came from broken-up bits of the Planet Sargon...")

Real stones have real energies. They don't need all kinds of fancy trappings to work. They just do. And unfortunately, most of the fancy trappings I've seen on vendors' sites seem to be accompanied by a price hike. So shopping requires keeping an open mind, but no so far open that the brain falls out.

JMO, YMMV (Your Mileage May Vary), and all that good stuff.