nope a 222 rem mag is a different case from a 223, has about 1 grain more powder capacity, but the bullets are the same. The 222 rem mag is the parent case of the 204 ruger, so there is an option for cases for reloading.
I think the ammo is still in production, but could be wrong, if it is, there's not a whole lot of demand for it so not many retailers will have it, anyone should be able to get you ammo though. here is a link to midway who carries nosler 222 mag ammo
http://www.midwayusa.com/browse/BrowseProducts.aspx?pageNum=1&tabId=3&cate goryId=19221&categoryString=653***690***
RR