Holders of an Oxford SSO can find all treaties published in the League of Nations Treaty Series (LNTS in citations) and theUnited Nations Treaty Series (UNTS) via a library within HeinOnline
Holders of an Oxford SSO looking for a pre WW1 treaty (for example with citations to CTS or Parry) should try OHT (below)
Holders of an Oxford SSO may find this compliation useful for the most important treaties
The laws of armed conflicts : a collection of conventions, resolutions and other documents by Useful websites available to all with access to the internet:
Travaux Prèparatoires of the Crime of Aggression by 
The Genocide Convention : the travaux préparatoires by Books with shelf marks beginning Internat 750 are on Level 3 of the Bodleian Law Library, one floor above the entrance level to the library.
The 1949 Geneva Conventions: A Commentary by 
Preparing for War : the making of the Geneva Conventions by 
The Anti-Personnel Mine Ban Convention by GCI Geneva Convention on Wounded and Sick in Armed Forces in the Field,1949
GCII Geneva Convention on Wounded, Sick and Shipwrecked of Armed Forces at Sea, 1949
GCIII Geneva Convention on Prisoners of War, 1949
GCIV Geneva Convention on Civilians, 1949
BWC Biological Weapons Convention
CWC Chemical Weapons Convention
CCM Convention on Cluster Munitions