Regarding some information, I could find about their habitat and ecology, that might come handy if you look for them in nature... As Darrel mentions, they are mainly to be found in strong flowing clean and oxygen-rich fresh but also brackish waters, also lakeshores where the water is moved by wave action. Living on hard substrates such as stones, old shells and occasionally on driftwood.
Considered in decline in Mainland Europe, but still very common in the Baltic Sea area in brackish waters.