Uranium supply is enabled by the tech Nuc Fission (NF). Supply increases for cities with lots of non-foliage rough land (Desert/Tundra/Glacier/Hills/Mtns). Bigger cities are more likely to supply it; cities of size 1-2 cannot. Demand is also enabled by NF, and is linked to number of techs you have, city size, and improvements (NucPlant and SDI). So ICSers who put their cities on plains or grass probably won't see much Uranium.
Oil is rare before Combustion (Cmb), and also increased by rough land (Desert/Tundra/Glacier/Swamp). For some reason Continent #9 was found to increase Oil supply as well. Demand is enabled by Industrialization (Ind), and tripled by Auto (Aut). It also increases by number of techs, city size, and improvements (Factory & SuperHighways), but MassTransit and RecyclingCenter decrease demand.