Not as shipments from the metropolis, but from the bar / tavern.
Something similar to how to hire mercenaries in the SC-2 wings of liberty campaign.
“The merc compound trains mercenaries hired in story mode with credits. The mercenaries are hired instantly at a mineral and vespene cost, at which point that unit type is put on a cooldown timer before it can be hired again.”
I think they should be support or complement units, not very expensive or cheap. But not very strong either.