Since many people said grass is the best for tortoise, I’d like to buy some grasses. Many pet store only sells hay. I also see some yard decoration company(e.g. lowes) sell lawns with real grasses. Can I buy that to feed the tortoise?
The pet stores sell little tubs of grass for cats to eat. It's usually kept right by the cash registers. It's live grass growing in little 3 or 4" tubs.
If you go to a feed store that caters to horses and cattle, you can ask the clerk if you could bag up some of the 'leavings' off the ground around the grass hay stacks. They usually allow that. Maybe charge you a small fee, or maybe just give it to you free. Before you offer it to your tortoise, put a small bit in a bowl of water and allow it to sit a while and rehydrate. Then rinse the dirt off and feed it.
Like Yvonne said, the big chain pet stores sell little plots of sprouted wheat grass. Some grocery stores sell it too. If you keep the little plots watered and in a sunny window sill, you can get 8 or 9 cuttings from them. I never tried it, but if you repotted it, you might get even more cuttings.