Does 200A max SCT-019-000 suitable to be used in the emonTx? What are the calibration coefficients I need to change? I need 200A and Wider CTs, the other CTs in the Use in North America table are hard to get or expensive.

When you read the data sheet, you will see that the output current is 33 mA per 200 A of primary current.
You will need to change the burden resistor in the emonTx - it is large SMT resistor marked “220” immediately behind the socket, and there are holes at each end for the wire-ended resistor that will replace it. You calculate the value from Ohm’s Law: you need not more than 1.1 V at the maximum current you want to measure. If that is 200 A, then the resistor is 33 &Omega.
The calibration coefficient is the current that would give you 1.0 V across the burden resistor, so you calculate the secondary current that gives you that voltage, then work backwards through the c.t., since you know the current ratio (200 A : 33 mA), to find the primary current.