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The 2SK30A datasheet shows that Vgs for 1mA is around -1.5V so using a 1.5K resistor is good for a start.
However, each one of 2SK30A could differs a bit and you'll need to trim the resistance to get an exact 1mA.
Also you have not shown in your circuit what sort of voltage is across the CCS. The 1N5297 is a 0.5W rated current regulating diode while the 2SK30A max Pw is only 0.1W.