Hi, we live in Spain & guess what? You can't find Seville oranges anywhere for sale here!
We couldn't even find any Seville Orange trees to buy anywhere here to plant!
It is orange season here at the moment & our trees have lots on. I use normal eating oranges, which we grow to make marmalade & it tastes nice, just use less sugar so its not too sweet.
Hopefully you will find some in the shops soon, good luck.