There are dozen, maybe hundreds, of supplements out there for tortoises; for the most part, they're not needed if you're providing a varied and appropriate diet for your tort.
Living in New Hampshire with tropical and desert tortoises means that although I'd love to, I cannot always provide the perfect diet or environment year-round, so I am sometimes forced to supplement.
When needs must, I have chosen to make my own supplements, not because I like making my life trickier, but because I wasn't crazy about the options out there (by which I mean on Amazon or in my local pet store... the ingredients in the generally available supplements are legion, suspect, and often unknowable.
To combat those specific problems, I make mine with as few ingredients as possible, high-quality organic ingredients that I would use on myself, and comprised of simple ingredients that I can easily pronounce.
Challenge: Wintertime lack of weeds and flowers
The biggest challenge facing a keeper of tortoises, especially in NH, is that the weeds and flowers that my torts love to eat in the summer months are dead and/or under snow for much of the year
My answer to that is a mix of plant matter I know is great for any tortoises, which I shake over the mixed greens I feed my creep in the winter months; it's comprised of: moringa, echinacea, wakame, calendula, nettle, chamomile, raspberry, rosebuds, dandelion, hibiscus.
It's presence in their morning salads a few times a week increases the nutritional value of the greens they're eating by a lot.
Challenge: Calcium deficiency
Many of the plants they'd be eating in the wild contain more calcium than they get from the diet I can offer my tortoises year-round, so I need to supplement their calcium intake, especially with the females who may be laying eggs.