Just wanted to post an efficient way to work toward this.
You can play survival mode on the map "Pain Garden". The second wave is always 40 gunships. I just restart after the first two waves. I use the wallagis war hound missile launcher because it locks onto two targets a time. This method is especially useful for people planning to complete the game. By dong this method you will be working toward your 100 and 500 waves played as well as your 10k kills in survival.
An alternate method if you want to grind it out faster is to load up 3-1 and reach the part with the huge drop ship with four circles on the bottom instead of two. This drop ship spawns tons of gunships, just be careful not to shoot at them until the drop ship is closed. If you don't destroy the drop ship it will spawn gun ships until you do.