Are you looking for all guns - Flak, Arty, AT, rockets - or just artillery. Some came in wicker boxes, some wooden crates, some metal cannisters, etc. There were different rounds in the same size and often the rounds were packed differently for each different type of gun in that calibre. Narrow it down to what you need and we might be able to help you.
Many aftermarket manufacturers produce crates, etc. Academy produce Allied and German Tank accessory kits that have rounds and crates for several tank guns. AFV Club produce a set of rounds (shell, bagged charge and casings) and support cases for the 105mm LeFH18. Can't go past those and you would be nuts to try and scratch build them. For Sig 33 and Pak 40 see http://www.tigermodels.com/shop/tmd/4 for some ammo and wicker cannisters. They may seem expensive, but you only need one set to use as a master and get the measurements for.