Use one of the dac's from one of the many companies that make them (e.g., Analog Devices). You don't have to use a 14-bit dac; you can always use one with higher resolution. For example, you can use a 16-bit dac by connecting the dac's two least significant bits to logic 0 and connect your 14-bit data bus to the dac's 14 most significant bits, thus turning it into what is effectively a 14-bit dac.