Retain an entertainment attorney or experienced producer's rep to advise you and negotiate your deal. I have seen filmmakers give their premiere away to minor festivals and thereby disqualify themselves from major ones. You can play in the lesser festivals later. If you get turned down by an important festival, the worst that happens is that your suffer a small delay in your release plans. No one will know which festivals turned you down.
Some distributors sell at the Berlin market which is known for art films.
There are also television markets that many distributors attend. Distributors are hungriest for product when a market is rapidly approaching and they don't have any new inventory. This is the time to approach them. But don't approach them too close to the start of a market. The bumper editions of the trade papers usually have an ad deadline of 3-4 weeks before a market.