Those look very similar to the Starrett Trammel set...
http://www.starrett.com/download/314_p361_364.pdfStarret makes expensive, but very good tools. Their trammel set (not just the points, which are sold as well) is $68. The eBay item copies the Starret design with some small changes to avoid litigation.
I'd not put too much stock into the claim of working with markers other than pencils.The pencil holder is meant for things of pencil size, and most markers are larger in diameter than pencils. While I don't have any crayons to measure, I suspect that they'd work OK because they are approximately the same diameter as a pencil. One possible issue could be crayon breakage. They aren't stout.
These are meant to be clamped to a piece of wood in use. For the large circles in figures, that means a long piece of wood. I brainstormed a bit for extendable items like radio antennas, but couldn't come up with something that would be easily available.
BTW, if you do a search for "trammel" on Amazon, you can find some really inexpensive versions. One from Grizzly industries (an importer of inexpensive tools) is only $7...
http://www.amazon.com/Grizzly-H5876-pc-Trammel-Set/dp/B0002U8BSG/ref=sr_1_12?s=gateway&ie=UTF8&qid=1285199220&sr=8-12From the feedback, the only complaint is one I've already mentioned - it's made for pencil-diameter markers and won't work with Sharpies, etc.