How to find replacement crank arm?
To find a replacement, there are a few details that you need to get from your current crankset. The most important one is to find what the bottom bracket of your bike is. You may need to remove the crank arms to work this out. 

Next, you need to know the bcd of the chainring to ensure that it will fit on your replacement crankset. Also verify that the four bolts are evenly spaced on the chainring, as some brands like Shimano change their bolt spacing in a way that is only compatible with Shimano cranksets or a select few third party cranksets designed to take Shimano chainrings. 

Lastly, purely for bike fit reasons, you'll want to ensure that the replacement crank arms are the same length. While the arm of your current crankset might be 200 mm, that is not the measurement that you need for this. To measure crank length, you need to measure the outside of the crank arm from the centre of the spindle to the centre of the hole for the pedal. This measurement should be between 170 and 175 mm on almost all standard bikes.