The Contractors those whom provides services to the US military and NATO, can access the NUCSIFs form here: https://ard.gov.af/file_download/287/NATO%26US+Contractor+Supplementary+Information+Form+v2.pdf
According to the BSA and SOFA, the tax exemptions is issuing as the contractor fill the form shall send it to the KO contract officer, and the KO sends it to the RS, and after the validation and stamp, the form sends back to the MoF by our associate.