Our company ordered the stamps from Viking, but the website is in Dutch and you have to register first. They have all kinds of office supplies with reasonable prices. You can order on line and they will deliver the second day, which is very convenient.
You can go to the above link to seatch for the article. It is easier to call customer service number 0800 8454640 from 8:00 to 18:00 for questions.
Good luck!