I know exactly what part you're talking about, and it seems like everywhere I go people are pointing me to totally different parts. Mine actually caught fire at the connection point nearest the mounting plate. I can not find one anywhere...I've been looking all over the place. No word at all from DJI who seem to be completely ignoring the many people with this same issue. The sad part is it would likely be a 10 dollar fix...I'd even pay 30 or 40 dollars for a new cable...I'm likely just going to need a new gimbal, but every gimbal i've found has VERY mixed reviews ranging from not working at all, to a little finicky, to being perfect. If ANYONE has found a solution to this or knows where to get a working replacement please let me know.
There are no replacement parts for the H3-2D gimbal. So you are only left with one choice and that is replace it with either H3-3D/H4-3D gimbal and modify the hole if you have to to fit the gimbal motor into the P2. Now if you're using a GP hero 3+ you can also modify the H3-3D gimbal so that you can plug the GP in the 30 pin connector that you used on the H3-2D gimbal. There is a video on YouTube that will show you how to modify the gimbal and the 30 pin connector can be found on ebay.