The National Electrical Code does offer tables of ampacities, including those for insulated conductors or wires and for conductors in air. A version of the tables for copper, aluminum and copper-clad conductors is available at LugsDirect.com.
Many electrical supply companies provide copies of the relevant NEC tables, in particular NEC table 310-16, online to allow customers to choose the right types of wiring for their needs. These tables list the allowable ampacities for wires at a range of temperatures so that customers can select the correct wires. Reading the tables can be complicated, but NEC table 310-15 gives further advice on this.