Hi Guys
There are a huge number of warbirds still flying worldwide - in fact there are over 50 airworthy spitfires of various marks, including I believe over thirty in the UK alone! In fact, there was a formation of around 15-20 spits flew at one of the Duxford shows a few years back. I'm not sure how many Hurricanes are still airworthy, but it must be about a dozen worldwide with the majority in the UK and Canada. Numbers of airworthy warbirds are growing rather than decreasing as more and more are restored to flying condition. However of major British aircraft there are many notable exceptions/shortages - Lancaster - 2 (1 UK/1 Canada); Mosquito - currently nil airworthy; Halifax - nil; Wellington - Nil; Beaufighter - several under restoration, etc., etc.
There would appear to be no shortage of most US types.
As for the Axis aircraft from the film, as Polar says, these were all ex-spanish airforce license-produced Me Bf-109s (Hispano Buchon) and Heinkel He-111s. although a few of the Buchons are still airworthy, non of the Heinkels is currently airworthy although a few are under restoration. There are a few (maybe 3 or 4) genuine airworthy Bf109s - there was one in the UK, although this crashed a few years back almost killing my old flying instructor (ACM Sir John Allison).
Amazingly - repro warbirds are also getting big now - a firm in Germany is making 6 new-build Fw-190s exactly as original except for Chinese radial engines; New Yak-9s are being made in Russia, and six Me-262 jet fighters have been built in California.
This is only the tip of the iceberg.
If ther were to re-make the BoB now, it would be a much easier taks, but it was probably this film which launched the UK warbird movement.