You can get a guaranteed GENUINE British army basha from New Cross Army Surplus, Manchester. I've used these guys many times before - they're not the cheapest, but I guess you often get what you pay for. Plus, they've been in business for ages - one of the originals!
http://www.militarykit.com/
Tel: 0161 834 18 18
Don't think they have any bashas advertised on their website, but I'm fairly sure they have some in stock (was speaking to the owner, Steve, about this very subject last month).
G