Unless you need a large number of shunts I would recommend to buy one. 200mV is an unusual value for a shunt. 60mV is the most common value, but I guess any manufacturer offering 60mV shunts will be able to supply one for 200mV. If the current you need is below 20 A you may find standard resistors suitable for that application.
The standard method for manufacturing shunts (up to 15000 A) is to braze rods of resistive alloys (with low TC) between two copper busbars. Later the shunt is calibrated to the nominal value by removing some of the resistive material e.g. by milling.
Can make shunts out of practically any conductor. However most conductors change resistance with temperature. Stainless steel changes resistance less than most conductors. Have made shunts from stainless steel welding wire and for higher currents have made from stainless steel banding straps.Operate shunts at low temperature to prevent change of resistance during operation.
did not indicate at what current you were wanting to obtain the 200mV. Empro is a high quality precision shunt, with minimal drift. (No I do not work there. I have personally used their shunts for DC currents from 5 to 1000 amps for over 10 years).
I would reccomend that you only use 50% of full scale when choosing a shunt. For example, if you need 200 amps, I would select a 400 amp shunt. This will provide you with less error due to self-heating.
