I travel all over San Diego County. Right now I don't see any leaves on the vines at all. At least none that I would offer to my tortoise. Plants will be in most of the garden stores in a month or two. I wouldn't pick leaves for my tortoise from just anywhere. At least not for his regular diet. I have a couple of plants, started last year from cuttings from a neighbors vines. They root very easily. This way I know what is not in the plant, meaning fertilizers and pesticides.
My sulcata loves grape leaves. He also loves mulberry leaves. I see mulberry and fruitless mulberry in more neighborhoods than I see grapes. They too are dormant this time of year.
Yeah, so grapevines, Vitus vinifera, the European or noble grape are a type of plant that will drop their leaves in the winter (deciduous). The leaves drop because of variation in day length, not so much temp, wind etc. So less the few vineyards literally in the tropics they all drop their leaves in the winter. This species, and the thousands of cultivars derived from it are grown everywhere but Antarctica.
Grapes are a liana, growing as much as 30 feet in a season. You can keep a vine in a container, bigger is better, and harvest your own leaves. A thirty gallon pot with sandy loam, and you could probably actually get a small harvest of grapes too. But if you mostly want leaves, remove the grape clusters so the plant does not dedicate energy to fruit production, you will get more leaves.
With the exception of organic vineyards (in San Diego for table grapes) you should avoid pinching leaves from the road side of a vineyard as grapes are heavily managed with chemicals, one of the most intese use of chemicals for any permanent crop plant. Always see if you can engage and get permission from the farmer/rancher before that pinch, maybe the will help you further than just a few leaves. Remember people who cultivate plants and animals are of a common mind, more than less.