How can you get the amoeba?
The time-honored way to study protists, as they are now called is to take a sample of water from a local pond or lake that does have wildlife- grow a so-called hay infusion and after the incubation period , sample the water under a microscope. This is basic Biology-l stuff. The Amoeba and the Paramecium, which has a shoe-shaped body something like Manhattan Island ( so I observe) are common residents in such an infusion. There are a number of books on basic biology which should prove helpful.