Finding and growing food is the best place. Grocery store greens are okay as part of a varied diet, but weed, leaves, flowers and succulents of the right types are best.
Here in California, it's easy for me to grow my own weeds, succulent, and flowers to feed to my tortoise. Every climate is different. Look at the section of the forum "diet and care". That will tell you some of the many things your reptile can eat. I like to see other's gardens and flowers they grow to see what is possible for my climate.