You can also write a list of plants that grow around you and those that you can buy and look them up on The Tortoise Table. It explains what is and isn’t suitable and why.
Mulberry leaves
Grape vine leaves
Hibiscus leaves
African hibiscus leaves
Blue hibiscus leaves
Rose of Sharon leaves
Rose leaves
Geraniums
Gazanias
Lavatera
Pansies
Petunias
Hostas
Honeysuckle
Cape honeysuckle
Leaves and blooms from any squash plant, like pumpkin, cucumber, summer squash, etc...
Young spineless opuntia cactus pads
Sites possible of interest in the UK include the Tortoise Lady; she has a long list of foods she considers appropriate, along with how often they can be fed; plus tons of other info. http://www.tortoiselady.co.uk/page8.htm. She also sells some supplement foods; seed mixes, and opuntia cactus pads if you’d like to try growing your own.
Shelled Warriors is another site that sells seed mixes and supplement foods; they also have a photo gallery of common weeds on your side of the planet. http://www.shelledwarriors.co.uk/site/Welcome.html