From Animal Crossing City

Crazy Redd's is a store run by Redd, a racoon-like animal who has a shifty appearence. He opens his shop about once a month, and he will send you a letter a few days before hand telling you when he will be in town. To find the exact place where his shop is, ask at the police station.

Most things that Redd carries are items you can easily find at Nook's shop, and are much more expensive then what Nook will charge you for. However, on occasion he will sell rare items that you cannot get at Nook's.