Vader9900 has really good little set pieces on ebay! He has dope dio displays too!
Marauders is the bomb someone else mentioned it, johns the best ships super fast!
Like dan said just everywhere! I have been collecting dio pieces for about 10 years now. I even buy other toys I dont want just for there pieces! Lol antique shops are a great place as well! some of the best pieces are found in the cheap prankster section at stores like spencers. Ive found a toilet key chain, the tubes and pipes I use for dios are actually build your own straw tubes just be creative! I great place for Ideas is stormthecastle.com as well as everyones pictures here!

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"All things are subject to interpretation whichever interpretation prevails at a given time is a function of power and not truth. "
Friedrich Nietzsche