The United Nations Office on Drugs and Crime offers a variety of data sets available to you, including firearms trafficking:
Data is available for review and download, including:
The Stockholm International Peace Research Institute (SIPRI) is an independent international institute dedicated to research into conflict, armaments, arms control and disarmament. Established in 1966, SIPRI provides data, analysis and recommendations, based on open sources. They offer the following databases:
The SIPRI Arms Transfers Database shows all international transfers of major conventional arms since 1950 and is the most comprehensive publicly available source of information on international arms transfers.
SIPRI Mapping ATT-Relevant Cooperation and Assistance Activities Database
The SIPRI Mapping ATT-relevant Cooperation and Assistance Activities Database provides information on cooperation and assistance activities in the field of arms transfer and small arms and light weapons (SALW) controls. The database supports states' implementation of the 2001 UN Programme of Action on SALW and the 2013 Arms Trade Treaty and includes activities carried out since 2012.
The SIPRI Arms Industry Database contains information on the 100 largest arms-producing and military services companies.
SIPRI Multilateral Peace Operations Database
The SIPRI Multilateral Peace Operations Database offers information on all multilateral peace operations conducted since 2000, including statistics on personnel, country contributions, fatalities and budgets.
SIPRI Military Expenditure Database
The SIPRI Military Expenditure Database gives the annual military spending of countries since 1949, allowing comparison of countries’ military spending in local currency at current prices; in US dollars at constant prices and exchange rates; and as a share of GDP.
The United Nations Office for Disarmament Affairs Military Expenditures Database offers military expenditure data for country by year, broken down by category. You can connect to the full database here.