Retrobiking is more of an underground thing here and the larger distances between places is also a factor to consider (geographically the UK is pretty small in comparison).
There's a small retro scene here in Hobart and the odd retro ride/gathering, but I can't comment for the rest of the country.
If you make it to Tasmania in your travels drop me a line as I'll be able to show you some of the best tracks/trails we have to offer.
A word of warning though, not a lot of the riding is truely retro friendly (well not in Tassie) so a modern dual suspension bike with disc brakes would be a wise purchase when you arrive.
Andrew