If you find that the dog becomes frustrated when you begin using other motivators, go back to using a higher ratio of food treats and decrease the ratio of food treats more slowly in the future. You want the absence of the food to motivate the dog to try harder, not to frustrate it into quitting. Clickers are a handy size, however, and easy to carry around. Very few major pet supply chains carry clickers. Instead, you'll have to get them through specialty shops, at dog shows, through clicker trainers, or from the Web.
Some people use other tools instead of the clicker.
Whistles, for example, are used frequently by people who are training animals to work at a distance. Flashlights are used by people working with deaf animals. If you choose a verbal marker, choose a sound like a cluck, rather than a word. Some dogs are afraid of the sound of the clicker. There are a couple of solutions to this.