I'm surprised they are not more widely bred and kept in the uk, they are just as colourful as darts and don't kill each other which is a pleasant change from some species. Wc browns seem quite common in wholesale atm and cb from Holland are available commercially but uk breeders are thin on the ground. Decent care advice seems to be solely in the hands of Marc from Dartfrog , with the occasional wanabee expert regurgitating his care sheets. I'm in the process of tracking down a couple of experienced mantella keepers who have little online presence to get some help, you can't beat info from knowledgeable keepers with practical experience of keeping, breeding and raising a species rather than well read self proclaimed"pros".
