You may possibly want to consider planetary ball milling ― the following RG discussion addreses that (powder) milling and homogenization technique: https://www.researchgate.net/post/Volume_of_PCAs_in_Planetary_Ball_milling

For getting the metal alloy paste of two different metal powders you can go through the well known solid state method (grinding, annealing, quenching etc). An alloy is defined by its metallic bond nature. It can be a solid solution of metals or a mixture of two or more metallic phases.

A metal alloy paste consists of the alloy powder and an organic binder. Usually an alloy paste is used for brazing. Look at the supplier :http://www.wallcolmonoy.com/products-capabilities/brazing-alloys/brazing-aids/. You can use the cement or the water soluble S-Binder. The requires viscosity you achieve by the right mixing ratio and  possibly by adding an organic liquid.