We can sell you one if you use our contact form or email our store to request it.
However, it really isn’t recommended for anything except the brushless servo. The main reason is that it increases the power draw of the pen lift servo. It’s potentially enough to exceed the capacity of the regulator that drives it, and/or enough to leave too little drive power left for the XY motion. (It also can reduce the lifetime of brushed servo motors.)
The brushless upgrade includes an upgraded power supply and does not use the voltage regulator on the AxiDraw control board, so it does not have these concerns.
How much weight can the Z-axis motor on a stock AxiDraw V3 handle? I want to use a paint marker like this: https://s.click.aliexpress.com/e/_DDPMkHV
…but it needs quite a bit of pressure to work. I thought of adding a weight to the pen, but I don’t want to burn out or otherwise damage the servo on the upward motion!