[@Willy Vereb] The reason they don't have a massive supply is that they don't produce much.
And I was thinking their personality might solve that a bit.

*Bellakee arrives in system*
-"Hello locals, we are here to trade. We can offer a multitude of things but our most popular is our ultra-fine Eltreum."
-"Ah, we have these awesome weapons and rare ores."
-"That's nice, now what do you offer for the Eltreum?"
-"Errrr, we want to sell you weapons..."
-"Oh, well you see weapons don't hold much value. Do you know anything of the Builders?"
-"Errr, we don't think so."
-"Too bad."
*Leaves*
*Bellakee arrives in neighbour system*
-"Wassup Bellakee, we found a satellite which might have been a Builder satellite, we also want to sell you some really shitty art and poetry."
-"Oh, very interesting, we will trade you [unexpectedly much Eltreum] for that."
*Leaves, while the first place thinks WTF???!?!*

Sure, my dudes could sell weapons to the next nation they come across, but it'd be a hassle. Since they'd see little value in it and it takes a bunch of space.