I haven't seen a true template, but it's fairly easy to add text to a PDF using an editor.
You'll need the correct heavy cardstock to print the 8x8" cards on. It's free, but they normally only ship them to agencies, as they're 1,000 count boxes of blanks.
If you wanted to print on normal unfilled FD-258 cards, you'd need to remove everything except the data you want printed, so it wouldn't double-up the lines and existing text. I guess the easiest way would be to import the "template" PDF as the background, place all text data where it needs to be, then delete the background. Make sure it's spaced properly for the true 8x8".
If I was going to go through that level of effort, I'd go ahead and scan a completed form, crop the prints and all my data, and save that PDF as a personal "completion" template. That way I could easily reproduce as many complete FD-258's as needed, on demand. Just sign and done.
https://www.fbi.gov/file-repository/standard-fingerprint-form-fd-258-1.pdf