Get a picatinny riser that uses clamp with thumbscrew(s) on the LEFT side of the riser. Then, use thin sections of any sheet metal with good compression strength (such as aluminum, brass, or mild steel alloy) to form V-angle shims that you will insert on the RIGHT side of the clamp. This will shift the riser and anything mounted to it, to the RIGHT. When you achieve the windage alignment you need, you can epoxy the shims in place (on the clamp) and you're done.
Don't stack shims for the final application. Get the sheet metal in the right gauge / thickness.
Otherwise, there are the scarce, Picatinny rail adapters (with M1913 rail on top) that have click adjustable / micrometer adjustments for both windage and elevation, but are pricey -- around $500 - $600 U.S.
IR-V