Follower headroom question
Looking at your circuit 







simulate this circuit &ndash; Schematic created using CircuitLab

I see that you have set the gate voltage at 

$$V_G = V_{DD} \cdot \frac{R_2}{R_1+R_2} = 225V$$ 

Therefore the voltage at the source will be around \$ V_S = 221V\$. 

This means that the voltage at the source can swing up from \$221V\$ to \$300V\$, only by \$79V\$. 

The negative swing is limited by the \$R_S\$ resistor and \$R_L\$. 

$$V_{MAXneg} = V_S \cdot \frac{R_L}{R_S + R_L} \approx 73V$$    

I hope that now you can see what you need to tweak to get desired voltage swing at the output.

At first, you could try \$R_1 = R_2 = 1M\Omega\$ and \$R_S = 3.3k\Omega\$ 

And do not forget about the power dissipation in transistor and in Rs resistance.  

Also, have you considered the push-pull follower instead single-ended one?