If you are missing diamonds in different colors for your Diamond Painting, you do not need to worry. There are ways to solve it. First and foremost, you should contact the store where you bought the painting to get these. If for various reasons you do not want to, I will tell you here about three ways to find missing colors.
Ask on Facebook
There are many different Facebook groups about Diamond Painting and many members save their leftover diamonds. Most are also usually very generous and at the postage cost give away diamonds. So if you are missing a few colors, it is definitely worth asking in any Diamond Painting group if anyone has and can think of giving you some. Sometimes the shade can differ due to different color baths, but if there are only a few diamonds, it should not be noticeable.
Use a similar color
If you have saved diamonds from previous projects, you can use a DMC color chart or a website to produce the nearest similar shade. Often there is a color that is similar in color and if there are only a few diamonds, you can replace them with the color that is similar without it being noticeable. You will get use of your leftover diamonds and save a few bucks on buying new or paying shipping to someone on Facebook. You can read about a website that offers a shade look up tool here: Replace a color with the closest shade.
Order only diamonds
If you are missing lots of diamonds and you have difficulty finding colors you miss in other ways, it may be an idea to order only diamonds. There are several stores that sell only diamonds. They are usually sold by DMC color number and often it is the small bag with about 200 diamonds that is the number of diamonds you get.