I am looking for mens padded underwear to make the buttocks look
larger. Can you help me?

I've found several online sources for men's padded underwear:

International Male
http://www.internationalmale.com/product.asp?pf%5Fid=AC29zz&dept%5Fid=10680&subdept%5Fid=

ABC Underwear
http://www.abcunderwear.com/paddedbrief.html

Undergear (Boxer)
http://www.undergear.com/product.asp?product=ae21lashzz&dept%5Fid=120&An=103&A=1266&Au=RollupKey

Undergear (Brief)
http://www.undergear.com/product.asp?product=ac29zz&dept%5Fid=110&An=103&A=789&Au=RollupKey

Lambda Shopping (Boxer)
http://www.lambdashopping.com/shopping/showitem.cfm?ID=219&LocationName=Search%3A%20%22padded%20butt%22

Lambda Shopping (Brief)
http://www.lambdashopping.com/shopping/showitem.cfm?ID=173&LocationName=Search%3A%20%22padded%20butt%22

Wicked Temptations
http://store.yahoo.com/wickedtemptations/u458j.html

Butt for You
http://www.buttforyou.com/product.htm

Google search strategy:

Google Web Search: "men's" + "padded" + underwear"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=men%27s+padded+underwear

Google Web Search: "padded brief OR boxer"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22padded+brief+OR+boxer

I hope this helps you to find exactly what you need. If anything is
unclear, or if a link doesn't work for you, please request
clarification; I'll gladly offer further assistance before you rate my
answer.

Best regards,
pinkfreud