In order to match existing furniture you need as much as possible to finish the furniture the same way the existing furniture was done. If the existing furniture was finished with an oil stain and clear coated and you spraying tinted sealer on the new furniture it will have a gel stain appearance to it and look completely different. The easiest thing for you to do if it's an oil stain and clear coat is pre-treat some wood samples with a 50/50 mix of linseed oil and mineral spirits and take them with a sample of the finish to a paint store such as sherwin williams and have them mix the stain for you. They can take their wood classics stain and add colorants to it to match the finish. You can do it yourself but you would have to purchase several bottles of colorant such as cal-tint to mix it. It's just takes a lot of tinkering and testing on samples to match a color. If you could post of picture of the color you want one of us might be able to give you more specific info on matching the color.