Same thing with my new Azusa Tri-Stars and drum/sprocket assembly. The new rims had some wobble but the drum/sprocket was absolute pure garbage!
Fortunately the mounting area near the bolt holes on my Tri-Stars was fairly flat. The outer edge near the bead is where the wobble is more noticeable.
What I did was order a blank sprocket with a 1" center bore, drilled out the holes, and had some 1 1/4" spacers machined to space the sprocket. I used a bronze bushing (1" OD 5/8 ID") to keep everything centered. I'm using a clutch brake so I don't need the brake drum.
Note: The spacers in these pics is
not what I used. I had some longer and wider spacers machined.