No manufacturers fecommend hardening fixers any longer so few are made. There's a fixer from Kodak that comes with a hardener which you add optionally and Tetenal make a hardener.
I've used Kodak Fixer all my life and would consider nothing else. Still have pictures I made in 1971 on fiber base paper and they have not faded one iota. I plan to be dead in 25 years, so it looks they'll outlive me. At the rate they're going it will be 200 years before they start looking like a Mathew Brady photo.
For FB prints hardening fixers actually slow the wash rate after fixing. They can also interfere with toning. Many people use just a plain hypo fixer consisting of sodum thiosulfate and sodium sulfite for prints.