I always buy online. There's nothing like walking into a chemist and saying 'I'll have the biggest bottle you have of that stuff for treating scabies' for making you quite unpopular locally!
I use it annually and used to get it from the chemist - but they've stopped stocking it.
I got one last week from Hyperdrug but don't like it. its very watery and doesn't have the same concentration of BB in it. I'll use this one up but after that I'm going back to chemist online and get the 25% stuff which i 'dilute' with a bit of olive oil so it lasts much longer.