All Visio stencil links have been moved to our main website:  
http://www.extremenetworks.com/support/visio-stencils
Please use the links there to download stencils for your Extreme Networks products.
If there's something you'd like to see, let us know in the comments!
EDIT (Nov. 11):  Links have been updated.
EDIT (Dec. 18):  Updated Summit X link to include X460-G2.
EDIT (Sept 1, 2015):  Links moved to main site.  Updated SummitX to include X430, X450-G2, and X670-G2.  IdentiFi now includes C35 and AP3825.