Aren't they up in Lancashire somewhere, perhaps try the Netherlands distributor instead?
As far as cost goes, VB's form is usually the highest end of the price bracket for this type of system. I seem to remember a figure of ~£5 or £6k for a full system, but will happily be corrected on that.
A few people on here have fitted Firestone and Gliderite. There is some discussion whether the brackets for one of these are sufficiently man enough for the job though: a quick search for "tab380" and his air suspension concerns will provide some interesting reading.
Another alternative is Roadmaster, although this is a mechanical rather than air system.
What is it that you like the idea of: adjustability or improved comfort?
Edit: joboman, I see you're trying to do this on a six wheeler - let us know how you get on with it?
Simon