You have at least two opponents who each control at least one artifact.
({1} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Journey On either from your hand or from the command zone by paying ({1} magic symbol) and commander tax, if applicable, creating at least three Map artifact tokens and exiling Journey On with the ability to cast it from exile.
Activate Krark-Clan Ironworks by sacrificing three Maps, adding six ({C} magic symbol) .
Cast Kellan from exile by paying ({2} magic symbol) .
Activate Meticulous Excavation by paying ({3} magic symbol) , returning Kellan from the battlefield to your hand.
Repeat.
If you have at least three opponents who each control an artifact, once you have infinite mana, you may forego sacrificing the Maps, and you may use the Maps to put infinite +1/+1 counters on creatures you control.