Notiingham has an Army Surplus Store (01159864041) which sells pretty much anything you could possibly want & I dare say there are many more nationwide so I'm sure they could put you in touch with someone.
Don't know of any dealers of genuine WWII Willys or Ford jeeps, but you may find dealers who have or can get Hotchkiss M201which is a very close copy of the Jeep and built under licence if France. I think some are released every year if they have not all gone. Just search for Jeep-Hotchkiss and you will find some great sites.
Hi there is a massive army surplus who have all kinds of jeeps tanks and everything else in Riply just off the A38 to Derby i go there a lot and its massive also sell uniforms and alot of 2nd world war stuff. navy too also german stuff .hope this helps .