produce a file with the coordinates sorted lexicographically... first by X then by Y. split the list into your desired number. Whether the split is optimal depends on your point pattern and its distribution, which doesn't appear to be a criteria in your requirements. Another option, albeit a bit more difficult, is to produce a minimum spanning tree for the points, then prune the points on the branches into groups until your groups have been satisified. This produces a eucliean shortest path solution for each group
