Now this is an odd thing that i've had happen to me that i've never seen anyone else ever mention in regards to Iridium. Creating a Mystcraft world thats flat with endstone end world and enderstar feild and as long as you can get it stable... i apoligize for i have never actually nailed down exactly the way i did it and it took me maybe 4-10 tries to re-create it...
Anyways, if you fly around you will see Iridium on the surface, very easy to pick out... yes i said iridium... Its not like you see it every chunk or anything like that... but considering how jetpacks and MPS's work it doesnt take that long to move around and find iridium. Spending about 1-2 hours in there i found over 1 stack of Iridium. Maybe someone here has duplicated this better? I should point out the server had the Iridium probability put up to 30% which might of been a contributing factor... regardless, i'm sure you would find more raw iridium that way than any other.