It will be very difficult to find something that does not scatter X-rays. All materials scatter X-rays but the scattering increases with atomic number or the number of electrons present in the atom. So one can choose materials with smaller atomic numbers. Amorphous materials scatter almost everywhere in the reciprocal space whereas crystalline powder scamples scatter in the Debye rings. But single crystals in very specific directions and do not always interfere with the measurement of your sample. You should add some details of what samples you are measuring and whether the zero-diffraction plate is your substrate or sample holder.

This link to MTI is quite close to what you want

http://www.mtixtl.com/zero-SiO2-303025S1.aspx