Absolutely no one asked for this, at least that I know of. Despite that, here is a chart that has all of the enlisted ranks and your chance of getting it. Trials were done 20 times for each rank insignia and this was converted from an overly complex spreadsheet I made. Fuck, I need a life.
WoRrankchart.jpg
For the officers, I noticed that depending on the unit, you will only get one rank insignia.