I believe you can download it from the Radio by going to Read, Current Tab, and then saving the file, however this didn't work for me, I have someone elses original firmware though, here you go.\

I am also having issues with the custom firmware, I have the GT3B-0.61 firmware, I am trying to get the steering to both have the 150% end point, however I can only select the end point for steering right. It's in channel 1 and esc is in channel 2.

Can anyone help me!! Thanks!