You can purchase liquid vitamin D3 1,000iu per drop which is the preferred form of vitamin D. You could then add the number of drops that you require to food etc.
I use Nature's Life Drop of sunshine which is a fairly competitively priced vitamin D3 in a fairly large dropper bottle 2floz/60ml and available on Amazon. It quotes 5,000iu per serving which is 5 drops. I take more than this as I do not get much sunlight.