Mazuri makes exotic animal feed, so I know they have a ratite product line.
Most people mix up their own feeds though since the Mazuri feed has been found to be a bit lacking.
What age Ostrich are you trying to find food for?
Here in Texas the general consensus is to feed ratite chicks a mix of regular chick starter and chopped greens (collards, kale and so on) for the first few days after the yolk has been absorbed.. adding in layer crumbles for the extra calcium after a couple of days. Once the first week has passed rabbit pellets and layer pellets are introduced into the mix and the chick starter is removed until the chicks are eating just rabbit pellets, layer pellets and greens. (chopped apples, fruit and grated carrots can also be given mixed with the greens for added vitamins and variety if desired but it's not necessary).
After the first year we switch ratites over to calf creep feed since it provides them with better nutrition for egg production and "filling out" the muscle.
Texas was one of the largest producers of ratites when they were popular as alternative meat sources.. so lots of experimentation was made with feeding for proper growth (good sturdy legs and healthy birds) as well as reproduction (lots of healthy fertile eggs which had high hatch rates resulting in healthy chicks). They did start out with Mazuri feeds and found the chicks that hatched were weaker, they had lower hatch rates on the eggs (lower fertility) and more leg issues. Switching over to what is posted above seemed to solve the problems.
Others here on the board can chime in with their feeding regimes as well as results they have gotten. So I hope this helps.