What uniform you get depends on what scenario you are planning
for example if you are planning on portraying the 13th DBLE you have Narvik (french uniform), N.Africa and Italy (British desert) France 1944 (British BD unless you are portraying one of the 650 Ukrainians captured from the Waffen SS that were put in US gear due to them being in the Southern sector of the front) Weapons you can get away with US from Italy onwards, Thomsons, Grease guns, 30 cals etc.
Epic militaria are ok for off the peg stuff http://www.epicmilitaria.co.uk/section. ... b8a0f7141/
Spearhead on ebay also do some quality gear though I dont look at the US / Brit stuff often there.
hope that helps you some but as previously advised pop to the ww2 forums theres bound to be some experts on there
on a note about SOF I wont touch them with a barge pole!!! 5 uniforms Ive ordered 3 were wrong size never got the right one back and took 4 weeks to refund me!, one the stitching ripped out after hanging it up, another one 3 of the 5 buttons fell off first time on doing them up never good quality imo ......they also have a knack of holding onto your credit card details for a couple of weeks before telling you were out of stock!