Can a DAC produce only positive output?
DACs are conventionally single polarity and made bipolar with an Op Amp and bipolar supply.
Digikey has about 10% of its unique p/n's for DAC in bipolar (771 of 7441 , others are duplicates but currently stock only 335 of 2,472) That should be enough to choose from ;)
To appease others who might want to make a bipolar DAC.
 Falstad Sim
Proof 
Offset -5V from Vref =+5V of DAC . (Or any Vref used by DAC for lower supplies.
Gain =2 to generate +/-5V using a 0~5V sawtooth sweep and CMOS RRIO Op AMP using +/-5V supplies.