Re: 155 Wipers take a flying lesson!
You can get the blades from Halfords, but they probably don't do the arms.
I'd avoid the Halfords own-brand wipers. I have them at the moment, they're plastic and flex far too much.
I use 21" and 19" blades, but I'll probably swap to a npair of 21" blades when they need it.
Best place for the arms would be a breakers yard/ scrapyard. Cost about a fiver. From memory, you'll need a 13mm socket and a flatblade screwdriver (to get the dust cap off)
Hope this helps,