The quick answer is the Drosophila connectome isn't yet complete however we could point you to towards one of the groups working on the reconstruction work that might be able to provide you with an estimate.
If you could please specify the stage you are interested in (Adult/larval)? Also what data size you're interested in as the data can be output in various formats causing large variations in data size or are you simply after a number of synapses?
Dr Robert Court
Institute for Adaptive and Neural Computation,