Stores, on the whole, suck. So if you can order online, I would do.
You could try this:
Attends.
If you order on a Weekday before 2pm, they'll send them to you within 24 hours! With discrete packaging... and you can give them delivery instructions, so you can tell them not to knock and to just leave them somewhere.
I'm not sure how good attends are (haven't tried them yet), but I hear they're good. I know another British member gets them often...
I've heard people complain about the American attends, but our ones are meant to be good.
Or... You can try ebay! Probably less reliable then buying them from a proper nappy site though.