Lots of Manufacturers make DC to DC converters. for commercial parts you can just google it, lots of people make DC to DC converters and switching regulators for the non high reliability market. For high reliability parts you can check out places like M.S. Kennedy at mskennedy.com , they are one of a few high reliability hybrid manufactures that have DC to DC converters and switching regulators in their product line up. Do you need input to output isolation? Do you have any regulatory specifications you need to meet? Is this for personal use, commercial use, industrial, high reliability?