Ian,
There are still lots of Ferret spares which haven't come onto the open market yet, but they were surplused several years ago through MoD disposal sales and were bought by L Jackson & Co. A couple of years ago Jacksons had a tender sale and some of this stuff came up for sale. I am told they have quite a lot of stuff left over, sadly they won't deal with me or you and aren't interested in selling single items, or even sorting out what they've got.
Alvis were based in Coventry, before being bought by Vickers. Vickers were then bought by BAE Systems. The Alvis factory in Coventry was shut down long ago, and anything that was left is long gone. Ferrets have been out of British service for over 12 years now, and in that time many MoD facilities have been shut down or downsized. The Ferret spares will have been sold off at the same time as the Ferrets.
I live near to Chetwynd Barracks, previously known as Central Ordanance Depot, Chilwell. Lots of Ferret spares have COD Chilwell labels on them. Since I've lived here I've seen the place reduce in size by over 50%. Most of it is now a business park and housing estate. Anything which was in those sheds is long gone too.
I know you and other American Ferret owners seem to think we have vast stocks of Ferret spares, and yards full of surplus vehicles over here. The truth is there are very few vehicles left in restorable condition, if any. The dealers who had all the spares have sold most of it. Quite a lot of it has gone to the USA. There won't be anymore coming out so my advice is stock up now while you still can!
Chris