Local markets round here have had them for a couple of weeks. But you can always keep sevilles in the freezer. I have never had a problem making marmalade with defrosted sevilles. So buy an extra batch while you can.
I think you are too late now for Sevilles - we buy in January to make
our usual Seville orange and sultana wine! I think it used to be February for marmalade makers, but now it is early in January.
Monica K