Here is a list of names approved by the civil registry for people born in the City of Buenos Aires.
If the name you wish to give Junior is not on the list (Junior is on the list), you can fill out paperwork to have the name approved and entered into the master list. (Only it might take until the kid finishes high school to have the paperwork approved and meanwhile you will have to introduce the child as Pending.)
The web page mentions restrictions for any names you might dream up:
Prohibited names include those that "are extravagant, are ridiculous, are contrary to our customs, express political or ideological tendencies, or give rise to confusion about the sex of the person."
It strikes me as a little odd that there should be a master list of names, but what's interesting is how the list reflects the diversity of the population here. It goes far beyond the typical Catholic saints' names. On the list already:
- Llewellyn (I can't even imagine how to pronounce that in Spanish)
- Del Sagrado Corazón de Jesús