Tricky, check out 'craigslist' for a 'Prop Designer', also 'Gumtree' - I'm not sure whether that is just a UK based bargain site, so check that out. It might be a tough find to hit the charity stores, but definitely worth a shot, I've purchased numerous items from charity stores to use as props, mannequins, furniture etc.
It truly all depends on what it is you're looking for, and seeing as it's WW2 specifics, I'd say you're best option is checking all the local theaters as @Dreadylocks suggested, you may get lucky, they could have the costumes & props from previous shows laying around,. I can't see the theater folk turning you away if you're sincere about the thing.
Coming back to what i said about hiring a 'Prop Designer', they'd have contacts that would get you the gear in no time, just depends whether you're going to fork out the greenbacks- In the case of it being WW2, which is a popular theme, there's a chance the PD will be able to get a hold of the gear from contacts they have, without buying, or making them from scratch which will see you paying the fee for the (PD) and not the labor, saving you a hell of a lot.
www.shootingpeople.com
(SP) Will be your best shot, I've worked with a couple PD's from shooters, they cover the entire spectrum.
So the balls in your court, If it was me, I'd say scout around, make a few calls and see what you can beg steal and borrow. You've got the option of the PD if you're serious about the thing.
Best of luck man!