Dives need ore, rare ore, organics, or volatiles deposits on an unclaimed planet in the same system. A Union HQ can reach systems up to 6 light years away (Dives can technically reach 1 light year away, but systems don't spawn that close together). If a resource is available, it is supplied at a base level + the best available modifier. Ore and organics are base 1, while rare ore and volatiles are base -1.
EDIT: Sorry, got my wires crossed with something else; the base values are 1 and -1, not 3 and 1.