You may be able to scrounge old uniforms from vintage shops or Goodwill. Most larger cities have Army-Navy surplus stores where authentic uniforms can be purchased -- but these don't come cheaply.   You could also check with a nearby military base (if you have access to one) and ask for any "decommissioned" uniforms or fatigues (these might have stains or rips that need repair-- typically the insignias have also been removed). Also, try to contact a local theater or college drama department that has recently done "Biloxi Blues," "South Pacific," "No Time For Sergeants" or any other military-themed plays and either raid their stock or find out who they used as a source.

Good luck!

Just wondering how many uniforms you need? What is your time line..ie when do you need the uniforms.