I'm in western Iowa and I found it on my local PBS channel on Sunday's either at 7PM or 8PM. I have my DVR record it so I can watch it later and fast forward any commercials. They usually show it on a couple times the same show so if you missed it the 1st time you can watch it later. Also if you go to the PBS.com website I think you'll be able to watch it there too. I'm waiting for the Selfridge series to come back this year. They've been advertising it too.
Since finding out about the Downton Abbey series just this past year, I went ahead and bought Seasons 1-4 and then pre-ordered Season 5 from Amazon.com. Didn't want to miss anything. Am thinking about ordering the Selfridge series later.