I found this advertisement in a magazine from 1967:
And I also found mine that I have had since the late 60's or early 70's, shown below:
Here's a close-up scan. My, those are some bright fluorescent colors! I don't even remember when nor where I got it.
I am sure I have one or two smaller examples, too - somewhere! If I ever find THOSE, I will scan them and perhaps add them to this post.