Natalia, I bought mine from my colonics place. One of those health clinics springing up everywhere in the UK that do everything from colonics to acupuncture. At least you can get some advice on using it from people who are familiar with the procedure. I can't imagine standing in the queue in Boots and asking for it!
I think it's a bit more expensive to buy this way but at least you get to see the product. It probably is cheaper on line. Mine is called Irrigator and is German. Made by Frank