This comes up every so often, there are a few threads below, and a created idea. The main themes appear to be either custom shapes or colors. Either way its going to be a ''hack'' as these aren't currently directly supported/ (or advised) in Tableau.
Hope something there is helpful...
previously created idea >> http://community.tableau.com/ideas/1955
Fill patterns not avail in tableau. we can use the shapes here.
Could something like this also work for a map?