I thought they didn't have them because they got destroyed.Class 4 replicators are also a Big Deal though, to the extent that (a) the Cardassians, a very advanced civilisation, don't have their own, and have to ask the Federation for them, and (b) when they get stolen, it's not just a simple matter of shipping over a few more from storage.
On Bajor, there's very nearly a civil uprising over the allocation of replicator technology to agricultural regions in order to regenerate land viability. There are only a handful available, and losing one for a few months can make the difference between surviving and going bust.
Basically, domestic and commercial grade replicators are reasonably inexpensive, but scaling them up to industrial grade gets exponentially more costly.
Sure, Bajor had an issue. But, the Romulans have many, many planets outside of their homeworld. And, they had more than a couple of years to evacuate their homeworld as well. You'd think they'd have the capacity that after more than 14 years on a planet, they would at least be able to pave the streets and not live in shanty towns.
I guess it would have been too expensive to make more than one set.