There are foods which contain vitamin D, but in low levels.  I take a supplement every day of vitamin D which is available over-the-counter.  It is very important, however, that if the supplement comes in a tablet, you need to make sure that you eat/take something oily with it so that it can break down appropriately.  If the supplements comes in a capsule (already combined with a oil base) then you are fine.  Since you don't really want to get extra calcium, it would be fine to add a separate vitamin D dose each day.  Just keep in touch with your doctor and recheck blood levels after a few months to see if your vitamin D levels have moved into desirable levels for you.