This study was recently released by Oxfam. On the other side, a recent IHT article stated that the US is the leading supplier of arms to the developing world (in 2006), followed by Russia and Britain (for a total of $28.8 billion in 2006). Congressional Research Service also publishes a report titled "Conventional Arms Transfers to Developing Nations, 1998-2005"

Africa’s missing billions: International arms flows and the cost of conflict

Africa’s missing billions: International arms flows and the cost of conflict
Africa suffers enormously from conflict and armed violence. As well as the human tragedy, armed conflict costs Africa around $18bn per year, seriously derailing development. The most commonly used weapons in Africa’s conflicts are Kalashnikov assault rifles. The vast majority of these weapons and their ammunition – perhaps 95 per cent - come from outside Africa. To protect lives and livelihoods, the 2008 UN Group of Governmental Experts working on the Arms Trade Treaty must ensure swift progress towards a strong and effective Treaty. All governments have a role to play in ensuring its success.
Africa’s missing billions: International arms flows and the cost of conflict (pdf 427.2 kb)