I found a DIY pencil or toothbrush holder that calls for non treated 4 x 6 x 6 lumber? The Home Depot and Lowe's only carry 4 x 4's.
Look on the web also for 'turning blanks' for lath work.
a real lumber yard, or laminate it from smaller boards. You may need to cut down a 6x6 as, around here anyway, most places seem to have only treated 4x6's.