Well, of course a truly ideal current source does not exist, since it would have to provide infinite voltage for zero resistance. But approximations do exist, in various designs. Actually, a van de Graaff generator acts approximately as a current source, with a very high voltage across it. There are also various ways to implement current sources with, e.g., op-amps, using feedback principles (we will likely be seeing some later in the course). Physically, these look pretty much like other integrated circuits (chips).