An easy first choice for a vivarium plant is pothos, aka devil's ivy, aka Epipremnum aureum. It's a very forgiving vine that will climb up your vivariums walls and has nice sturdy leaves. It should be available nearly any place that sells houseplants, home depot, walmart, etc.

However, you might want to have a browse through your nearby garden centres, home depots and so on and see what houseplants are available near you. Take notes on the plants you like the look of and then research their vivarium/frog suitablity, then go do some buying.