If you need a local converter on a board you are designing, the output specs are quite in the relm of monolithic converter with datasheet/cookbook solution. So any designer willing to put some effort into reading should be able to make something functional for you. Meeting EMC, good layout, etc. may be a different story.
If you are looking for an off line solution, then I agree with the posters above. This is something you buy, unless there are very special requirements you have not shared.