By Sam Laskaris Writer They’re down. But not out. The Six Nations Rivermen lost their third consecutive game at the Presidents Cup on Tuesday. But members of the Rivermen are hoping they can still be one of the top four finishers after round-robin play and advance to the playoff portion of the national Senior B lacrosse tournament being staged in Oakville. Six Nations was defeated 8-3 by the defending tournament champions, the Ladner Pioneers of British Columbia, on Tuesday. With that loss the Rivermen are now sporting a record of 1-3-0. Six Nations has a pair of round-robin matches remaining. The Rivermen will face the Kahnawake Mohawks in a 5 p.m. contest on Wednesday. And then they’ll square off against the Tuscarora Tomahawks on Thursday, in a match which also…