Hello Capt. Phuong,
I have no experience with the Mi-172 but some on the 171 even if it has been some time now. I understand your frustration as the Russian system differs from the "western" one as they used to have CG lines painted inside the cabin marking how much could be loaded in a given area starting from the center (at least in cargo configuration).
As minigundiplomat pointed you could try some of the operators. Vertical de Aviación and Helistar in Colombia operates the 171's. We used a quick template to calculate take off weight and I believe also CG before every departure, unfortunately I have been unable to find a sample for you in my paper box.
Best of luck.
Modtro