There's no real way around this other than to get a crafted or reskinned version of something used for a later expansions content.

But you're right. Dungeon loot RNG is abysmal. Running Aglaia for the tank body piece has been a nightmare. How long has that been out and I've only seen it drop 3 times and never gotten it. I've also never seen the majority of the ShB and EW minions and orchestrion rolls that drop from dungeons either. Star Bird? Forget it.