<CitizenGenBaseTurns>10</CitizenGenBaseTurns>
    <CitizenRateReductionPerUnit>.2</CitizenRateReductionPerUnit>

Located in GC3GlobalDefs.xml

There are also a couple of intresting Effects that could/will grant units:

GrantUnitType

GrantUnitTypeAndPlace

CreateUnitOnPlanet

You get one every 10 turns. You can force them as well, though unless you have a powerful social construction planet you may be better off just waiting 10 turns.

There is this citizens breaking trick. Colonizer can instantly finish citizen project on newly colonized planet. This likely to be unintended behavior.

I think that's a superb idea.

Once you research a particular tech, you can recruit one on a planet (as a planetary project).  They are expensive.