Here is a list of approved dealers and products for purchasing reproduction WWII USMC Uniforms. This list has been compiled by fellow WWII USMC living historians and reenactors who strive for top quality in their kit. Part 2 will be field gear.
P41 Coats/Trousers Utility: The P41 Marine uniform was the standard combat uniform for most of WWII.
Undershirts: White T-shirt that was worm under the utility, khaki and wool shirt. White athletic T-shirts of the 1940s were cut different from modern T-shirts, most notably the sleeves and the collar. Caveat! Man the Line doesn't have the best Customer Service on their website, I suggest ordering from their shirt from their eBay page for protection.
Leggings: Its suggested that original leggings should be sourced for your impression.
Socks: The closest to WWII style USMC socks on the market.
Service Tags: The Marines, Navy and Coast Guard used a different shaped service “Dog Tag” that was different from the Army service tag.
Summer Service Uniform / Khakis: Shirts, trousers and Scarfs (neck Ties) can be sourced from this link.
Trouser Belt: Unfortunately, the WWII era USMC belt buckle is not being produced, an original will need to be sourced.
Caps, utility: The Marines used the army cap for the first half of the war, in 1944 the USMC switched over to their own branch specific cover with the EGA on the front.
Field Jacket (M41) For the later colder campaigns, such as Iwo Jima and Okinawa, the Marines used the army field jacket.