You cannot make your own with any degree of accuracy. Someone on this forum (I think it was grizzman) said that in general, EC/TDS meters are calibrated close enough so that we shouldn't worry too much about calibrating them.

If you'd prefer to calibrate for peace of mind, you can find the solutions with a google shopping search for about $20. Your meter probably tells you it's preferred calibration solution strength right on the stick or in the instructions.