Thank you so much for the helpMaidenhead Morden is a good bet. Else ADC in Balham area.
I got mine on Ebay, you can find some good sellers out there, I had no luck with breeding them due to my life being too busy to keep them maintained, but they are hugely beneficial for most tanks that can house them safely. Hope you find some and get some going. Personal fav is the basic cherry red.I live in Croydon and don’t have access to a car so any store nearby with connectivity to public transport would be great