I know someone who found it on the course when I was playing a round with him and said 'wow this is rare I don't want to loose this' it was a blue and white one but he couldn't resist playing it off of the next tee to see what it was like and being a single figure golfer he is usually pretty reliable to not loose a ball as if anything he only just misses the fairway. But as luck would have it, or not, he hit it in the long stuff and it was never seen again. We even let a group through looking for it. You can get them from ebay though if mad isn't selling his though. Talking to people who used them though they never really cut the mustard anyway.
you can get them for £2.50 from Ebay if you definitely do want one. Could you not make your own similar thing, get one of those alignment tools to put a line around the entire circumference of the ball and then colour in one side with a permanent marker- it would be a bit of work but nothing too hard. I like the concept of the idea though: using it for putting.
If you have one of these they could be valuable. I googled Ping two tone golf balls and in Ebay goldmine I go these prices:
Red / Silver - £100
Aqua / Turquoise - £60
White / Peach - £40
Green / Red - £35
Black / White - £30
Orange / Turquoise - £15
Pink / Blue - £7
There are hundreds of other combinations but any ball featuring gold, silver, or black will fetch a good price