There was a place on the internet, ToolsforCheap that had them, but i just checked thier website and not only do they no longer stock them but they are going out of business. My sugestion is to set up a search on eBay for "Atlas milling machine" and "Craftsman milling machine" and have them send you alerts. You may have to wait a while to find one that someone doesn't think is worth a fortune, but it will come along. Mine came with a 7/8" arbor and I was able to find a 1" arbor for it that way. It's unfortunate that that place went out of business, as I also got 3/4" and 1" shell mill holders from them as well as a set of collets for my machine. The collets are easy to find on eBay, but shell mill holders are not. Good luck.