When will apple restock refurbished Apple pro 3rd gen 12.9

Also you need to ask Apple about things like this. We are your fellow end users and have no more idea that you.

I can say it has been a long time since I have seen any iPad refurbs on the refurb page. It has looked like this for a long time:

+1 on stedman1's recommendations to check often. We buy a lot of Apple refurbs and, to find the model I want, I've often had to check hourly!

Apple’s refurbished stock of items can be very unpredictable. There is never a schedule as to what may be available, so if you are seeking a particular unit, checking repeatedly is the only way to find it. Sorry.