It'll be in the Netherlands Gavin (although there are now some UK producers). The main problem with bumble bee colonies even when native bees are used (which many are not) is, as you identified the spread of pathogens. Bees from the facilities that rear vast quantities of colonies typically have higher infection rates than would be experienced in the wild. They then go on to spread these pathogens with their wild living cousins. Reminds me of another species of bee we all like...