Pretty much every welding store will carry er70s-2, more commonly known as 'A15' in the UK (er70s-6 = A18). Not so many places stock it in sizes below 1.6mm though, Weldequip carries 1.0mm, Weldmet (based in Surrey) carry both 1.0 and 1.2mm but you'll have to buy in larger quantities than weldequips 'maintenance packs'.
The difference between them is in the deoxidising elements, explained in depth in this thread... http://www.mig-welding.co.uk/forum/showthread.php?t=22172&highlight=deoxidised
The difference between them is in the deoxidising elements, explained in depth in this thread... http://www.mig-welding.co.uk/forum/showthread.php?t=22172&highlight=deoxidised