How to get an Individual Taxpayer Identification Number (ITIN) as a non-US resident?
According to the IRS, you need to file an IRS Form W-7, IRS Application for Individual Taxpayer Identification Number.
To obtain an ITIN, you must complete IRS Form W-7, IRS Application for Individual Taxpayer Identification Number. The Form W-7 requires documentation substantiating foreign/alien status and true identity for each individual. You may either mail the documentation, along with the Form W-7, to the address shown in the Form W-7 Instructions, present it at IRS walk-in offices, or process your application through an Acceptance Agent authorized by the IRS. Form W-7(SP), Solicitud de Número de Identificación Personal del Contribuyente del Servicio de Impuestos Internos is available for use by Spanish speakers.
If you already knew all that, please give us more information on the problem you are facing.