Mapping Center Answer:

Not to my knowledge.  Jim Mossman has published a number of ArcMap symbol sets, including highway shields, but these have primarily been for seelct U.S. states.  Here is a link to many of his online symbols:

http://search.esri.com/results/index.cfm?do=support.index&start=0&q=mossman

And here is a link to his personal web site:

http://www.mapsymbols.com/ddv_products.html

However, you might not find what you need here.  So one thing you can do is find a graphic image of the sheild and save it in either .emf or .bmp format, then use that the same way you would a highway shield.  For example, I jsut searched on the Web and foudn this:

http://commons.wikimedia.org/wiki/File:Australian_Highway.svg

You coudl save it in the right format and then just replace another highway sheild with this one.