Here is a list of plants edible for bearded dragons; scroll down for those who usually can be bought potted:
Most herbs that are commonly used in the kitchen are edible for bearded dragons. You can get organic potted herbs in the vegetables section of supermarkets, or in garden centers. Easy would be e.g. parsley, lavender, mint... I have seen golliwog/ turtlevine plant often in garden centers, usually when catnip and cat grass are sold, it's also there.
Another option would be a garden center that ships, if there is really nothing where you live.
For those plants that aren't organic it's good to change out the soil, and then let them grow for a while before putting into your dragon's enclosure.
Another option that works often: Grow them. Even if you have no garden or balcony: Often they can be grown indoors on the windowsill.
What I do with live plants usually: If I want to provide a certain kind often, I have two of the same, one in the enclosure and another one to regrow. Once my dragon has eaten a significant fraction of the plant (i.e.: half of it), I switch it out and let the plant regrow outside of the enclosure.
