Looking for a dual hitch: cargo and spare tire carrier?

Be careful you don't exceed the tongue weight rating of your hitch. I personally would derate it somewhat for the cargo carrier especially since it is extending the lever arm beyond what a trailer would apply to the ball, which puts additional stress on the hitch...and frequently adapters/extensions recommend further derating of the hitch.

The main part you're looking for is probably a "dual hitch adapter." Etrailer, as linked by Ken, does carry them (and they're a good company to deal with).