Hi, all I shoot is the 243wssm. I purchased 2000 rounds of brass a few yrs back. I won't give any of it up, but the place I purchased them at was http://store.iqmetals.com. They have been out for about a year now but they have federal 223wssm brass. You would need a die to expand the neck a little bit and you should be good to go. Hope that helps.
I am in the same boat, just purchased the 243 wssm upper I have always wanted and then go to buy some brass and wouldn't you know it there is no brass to be found anywhere.
If anyone has any leads on some brass let me know.