According to the IRS website (Nonresident Spouse | Internal Revenue Service (irs.gov)) - under the Section "Social Security Number," you can apply for an ITIN by filing form W-7 with the IRS. I suggest that you visit the nearest U.S. consulate for assistance and to provide evidence of your spouse's identity, age, citizenship, residency, etc. so that you don't have to mail the documents to the IRS.
