You can download a blank W-9 form from the US IRS: https://www.irs.gov/pub/irs-pdf/fw9.pdf
We only need the first page of the W-9 form (the page you fill out), not all 6 pages.
To upload, scan your completed W-9 page to a PDF file, or take a JPEG (JPG) photo of the page, or if you are equipped to fill in and sign a PDF electronically, use that fully completed PDF file.
Or, you may mail your completed paper W-9 to: FSGW, PO Box 323, Cabin John MD 20818