Seville oranges for marmalade - how important is freshness?
I'm presuming that your'e British because (a) You want to make marmalade (b) your nickname is 'tea drinker'. am i right?

Anyway, those bitter oranges are grown not only in Spain but in other parts of the Mediterranean as well, but their season i relatively short - so if i were you i would keep my eyes open for nice ripe ones and buy them - you can keep them cooled for at least a month in your fridge if they are in good condition in the time of their purchase.

Tip #1: try to buy oranges that weren't waxed.

Tip #2: if you can get Satsuma Citruses, they will do a good job as replacements. The result might be a little more sour though.