Best to go to the Vauxhall dealer spares dept for them.
Check online stores and local motor factors for price but I found Vauxhall were only a few pounds dearer, well worth it for the peace of mind.
Also, other makes may not have the connectors for the pad wear sensors, which isn't hugely important but is very annoying.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.