Hope you got a sack full of magazines because they are going faster than the ammo!
I have some .223 brass I've collected for my future .223/5.56; mostly stuff I've picked up a a LEO range. Let me know if you can't get hold of some locally and we will work something out. Lot of folks don't reload .223 so you might check local ranges who sell the brass for scrap. Maybe even check the scrap yard. Know any other reloaders? Ask them if they could spare a couple hundred cases.
Crying shame to have a new rifle and no ammo