I would think that it is self explanatory. A spy agency is an agency that is engaged in spying.
A spy gets paid by the people or agency that wants the information the spy is looking for. If it's a government agency, then the tax payers are paying the spy's salary. If it is an industrial spy looking for a company's secrets, then the corporation that hired the spy will pay the bill.
Central Intelligence Agency (CIA)
The world's largest spy agency is the CIA which which gathers intelligence information about foreign governments.
nsa
The Central Intelligence Agency (CIA) was created in 1947.
The acronym CIA stands for the Central Intelligence Agency (US spy agency).
Apart from ASIO, probably. It would not be much of a spy agency if everybody knew about it.
If it were a real agency and they want you I'm sure they'll contact you.
cia
A spy? Apply to the Central Intelligence Agency or the National Security Agency when you're old enough.
CIA - Central Intelligence Agency
You get it from Doctor Spyglass, at Spyglass Eyewear, who secretly does research for the spy agency. (see the related question)