Any commercially grown plant will have fertilizers and/or pestcides that can be harmful to your frogs. From what I've read here, it takes about six weeks to prepare them for introducing them into a Vivarium.

My suggestion, (this is what I plan to do) is find someone that has a lot of houseplants, chances are they have rooted cuttings sitting in a glass of water somewhere. (Make sure they haven't treated the water)

Philodendron and pothos are both houseplants that are hardy, easily propogated and suitable for terrariums. I don't know anything about Brom propagation, but I will be reading up in the near future.