I bought a few WOS (World of Springfield) figures from eBay. The Kang and Kodos aliens, Moe, Cletus, Krusty, Otto, Apu.
I bought the Comic Book Guy with a "Worst Episode Ever" white shirt from someone here on Pinside (sorry, I forgot who it was).
The Kwik-E-Mart decal to go on the "base" of the upper playfield and replace the original generic looking sticker - I got this from Matt at Back Alley.
I also have the Duff beer can speaker mod but cannot remember where I bought it. Sorry.
Colored Cliffy's are the best on the posts for this game. I have hot pink on a couple along with a buffet of other colors and it looks cool.
Maybe that helps a little?