You could do it yourself with number punches if you know the correct location, font style and size.
I have three different sizes and styles in my toolbox at work but i wouldn't know if they are what you need as i no longer have a 'ripper'.
If someone on here could supply a picture of the serial number on their 'ripper' and measure the size i will see if i can match it with my punches
Let me know if i can help