SSNs are issued by the Social Security Administration for the purposes of keeping track of social security (read: government-backed retirement pension). The Internal Revenue Service keeps track of taxes and uses SSNs to keep track of all taxes (including payments into social security).

Some individuals (such as yourself) are not eligible to receive a SSN. For those individuals who need an identification number for US tax purposes, the IRS issues ITINs. See here for more information: https://www.irs.gov/individuals/individual-taxpayer-identifi...