Or should I say 'Deep joy and an empty bank account'?...
Having started to think about getting some spares for the TRW I have found the spares situation resembles that of the M20 from 30 years ago...
In other words most of it is available NOS from Canadian, French and Pakistani 'surplus stocks' via dealers who specialise in the model.....
Of course, like the M20 this situation won't last and in the nature of these things the 'fast wearing' parts will go first...
This is good news as generally I can get what I need...but it's bad news in that I should buy some of it now while I can...and of course I have an addiction to NOS parts so that doesn't help...
I must say previously I've only taken a passing interest in the TRW, but if you want a 'military classic' that you can use regularly and that still has excellent spares back up, this one should definitely be on the list...Ian 
['I think they are under-rated - falling in the tele/rigid/SV period no one is buying into.']...
True until relatively recently I would say...Current prices for the TRW and GB40 indicate a change has taken place though and there is growing interest in both bikes...
They are now being sought for what they are rather than what they can be made into...
I looked around for a short while at running TRWs and it soon became apparent that the days of the £1500-£2000 TRW are gone...
Good examples will now fetch double that and more with one (optimistic)dealer listing a low mileage example at £9000!!...
£3500 to £5000 seems to be a dealer price with £3500 at the lower end, so in fact, on parity with WW2 machines...Ian
So as I was saying...
...A new TRW cylinder still in its packing case..Note the May 1964 packing date...
The last year of TRW manufacture....Ian
"Current prices for the TRW and GB40 indicate a change has taken place though and there is growing interest in both bikes..."
And just when I am looking for a nice WD B40... 
email (option): d.stapleton78@btinternet.com
I would say personally the B40s are lagging behind the TRWs to a degree pricewise...and with both models it is still possible to pick up a bargain buying on the private market...
The only TRWs I found below £3000 needed rebuilding...
I also looked at the B40s and a couple of ex Home Office B31s...Both B31s were over £3400 whilst there were still some cheaper B40s about..
There's one on e bay at the moment for example, at £1515 with 2days to go....
I think part of your problem is that you are looking for a rarer version, not just a WDB40....Ian
Yes Ian, your right, the RAF B40s are hard to find, though they are out there. I know of two that have turned up fairly recently, which were purchased by acquaintances. I'm ever the optimist, one will turn up... eventually. 
email (option): d.stapleton78@btinternet.com