I find that the more you use a VX parts department, or any other supplier of aftermarket parts, the more obliging they are, and the better discount you get. I usually ring them up, speak to my usual parts chap, and as they invariably don't now stock parts other than routine service items, he rings me when its in and I collect when convenient. If there is any doubt about the actual part of fitment, he orders both and the one that isn't required he returns. It also has the benefit of him doing a more comprehensive search for parts instead of the CBA attitude some have if you are not a regular customer.
Within a 10 mile radius from me, there are two Vauxhall dealerships - one part of a multifranchise group; the other an independent dealership, both of which are very helpful, although the independent is more of a personal service of the two. The nearest other dealerships are 12 miles away and 25 miles away. If you travel around whether that be for work or otherwise, I try to combine the collection of parts with another unrelated journey.