Are there any 3D printing services or something similar to 3D print or injection mold light reflectors?
I'm trying to find something that is similar to PCB printing that allows you to upload a 3D design of a reflector and they will produce this reflector and coat it with mirror surface.
I would not recommend extrusion printers for this, because they are unlikely to produce a smooth enough surface. To get a clean surface, the irregularities have to be a fraction of visible wavelengths, which is to say on the order of 0.01 micron.
Without knowing what sort of reflector you're thinking of (flat? spherical? parabolic?), it's hard to recommend a specific optimal, cheap approach. All in all, you're probably best off looking in standard catalogs such as Edmund Optics.