@colonel-ace AAA guns are always welcome in China, but what I have a hard time buying is China taking back the road after retreating. If they simply retreat, that means Japan has lost few if any land units, and China will have no more than 3 artillery with which to attack an intact stack of Japanese land units which may or may not have 8+ planes stacked on top, depending on when they took the territory. China does better on defense than offense, and if the strategy is to retreat and take back land, I fear that China is doomed. The benefit of those 3 guns will be vastly outweighed by a large Japanese land army.
Enough doom and gloom. I agree with you that you want AAA in China, but the quickest way to do that is to send a gun or so up from India (unless Japan is going Calcutta Crush). As Russia, if you really want to help, send in a few fast movers like mechanized inf. to aid in a multinational stack, preferably in Yunnan if you can manage it. Buying and sending slow AAA from Russia will be too little too late, especially if China has done nothing but retreat.