Then why are used J frames here almost the same price as new ones at the store? Not buying it (pardon the pun).
Scarcity of the resource. Just because the used gun market is saturated, does not mean that every specific make and model is at a level of such saturation.
Revolvers aren't as popular as semi-automatic pistols and that's been the case for quite some time. And now you're referring to a very specific model within a niche market. So yeah, price is going to reflect that reality regardless of where you buy that revolver.