I can't find the thread, but a few years back, there was a discussion on where to get checks with GLO letters on them. While looking for checks, I found a site:
http://secure.checksinthemail.com/line.aspx?lineid=105&lid=B18.
They're pricy, starting at $19.99, but if you need the paper trail, they could be fun. Unfortunately, they didn't follow through on using the right colors for the right GLO: