From what i see on the net, Dark Iron looks similar to Gunze Sangyo's H76 "Burnt Iron" - you could give that a try.
I know Humbrol (enamel) and Tamiya (enamel and acrylic) make colours pretty much identical (to my eye) to that of Burnt Iron - sorry, can't remember numbers though.
Anyhow, those three brands are all worth a look too.
Chris.