Sorting is a good move.

One thing you can do is use bricks as bricks that they are not, for instance, for some bigger sets I'll use a slope brick as a wall brick.  I just have the flat side of the slope built into the wall, and then I have this ugly thing jutting out from the back part of the wall.  Of course, this awkward thing doesn't matter, as it won't be visible on the good side of the wall.

For a brickfilm I'm planning called Welcome to Darkmoor, I'm going to shoot in black and white and build a set with very ugly looking colours.  Or course, since it's black and white, I can use much more stuff on my set without having to bother as much with certain constraints.  For instance, I can have blue grass, but on camera it will look close enough to how the green grass does.

1) The Builders of Tomorrow Set has all brick-shaped elements in many colors.  One or two of those sets will increase your brick base.

2) Put an ad in your local trade paper: "Kids all grown up?  I'll buy their Lego collection".  I got a lot of older sets that way, which are heavier in basic bricks/windows/ slopes, etc.

3) Watch the Nathan Wells videos on sets.  You'll find a link in a recent thread on a similar topic, started by General Ned.