It is possible to keep mantella frogs in simple setups with a disposable substrate and fake plants. I keep all new mantella frogs that I recieve in plastic storage containers with paper towels for a substrate, fake plants, a shallow water bowl and a few dried leaves as hiding spots. I also maintained a golden mantella for over a year on a substrate of moist foam rubber with fake plants and a water bowl. The main thing to keep in mind when using fake plants and a disposable substrate is that everything needs to be kept clean. The substrate may need to be changed as often as once a week depending on the size of the enclosure and how many frogs are kept in it. Below should be a photograph of an enclosure that I keep a female M. viridis in.
The best place to purchase mantella frogs is from private breeders. Unfortunately, not all species are available as captive-bred animals and it may be required to purchase wild-caught frogs from a reptile dealer or pet store. If you need help locating a breeder let me know,

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Devin Edmonds
devin@amphibiancare.com
www.amphibiancare.com