Eruptor Mercenary not Spawning

I'm running a VFoS build and I'm looking for an eruptor merc to pair with it. I've run well over a hundred maps and have not gotten a single one. I could be getting unlucky, but at this point I feel like somethings wrong. For context, when I first started farming mercenaries I got eruptor mercs regularly, but after I got my first one and dismissed him I have yet to get another. I've hired other mercs such as ripper or earthshaker and still get them regularly even after dismissing them or not. Was wondering if anyone else has had this problem, any help would be appreciated.