I think I found a picture of it? It's the only thing on their website that looks like it.I think it was probably an aquatic insect in the family Nepidae, which superficially resemble scorpions. Although I find it surprising that a LPS would have these, even if they are an exotic specialist...
M. Giganteus? They're a speciality store for reptiles, but they started branching out into more arachnids.
I could be entirely wrong. They only had one on display in an aquatic tank with fake plants for cover/climb on, I believe? It might have been something else they already sold and removed from the site.
They even have rf baboons now, and had a Goliath bird eater recently.