Please rephrase your question.

Dear bob c

I need to some sample of changable circuit current source that i can change current from 4mA to 20mA.

thanks for your cooperation.

what kind of a circuit are you trying to build? What is the application?

Dear bwrench

I need to some sample of circuit current source that i can change current from 4mA to 20mA.

thanks for your cooperation.

Any simple circuit has a power source, a load, and a way to switch the power on and off. The current draw is determined by the load. In your case, you can use a variable resistor to control your variable current draw. I would think that the parts could be found at radio shack or any electronic parts supplier

I do not know exactly what you need but check this chip out: http://www.st.com/stonline/products/literature/ds/1318.pdf