[@Noxious] - Good question. 

They employ various methods. The most common is plying through the basic military for potential recruits, or drafting inviduals they think can withstand the introduction. They're only told the basics: that they will be helping the Govern. The candidates are selected carefully or noticed by something of their past that gives them some certain attention. It all bases in their origin I guess. The rich buy their ways in, wanting that power. The poor sometimes volunteer themselves so they can be of some value. Some are just.. "volunteered." There's quite a bit to work with.