There are only three Clowns to snatch Coupons from, road-block NPC dialog just makes you think there are more to be found. Talk to each to receive Coupon.
Afterwards NPC will spawn at central road, between fountain and Pokemon Center.
Clowns are located near Pokemart (east of fountain), TV Station (north of fountain), and Poketch Company (near western exit).
To open Poketch, click R (upper right shoulder button), Clicking R again will switch between small and full views. Hold R to hide it. Button on right side of Poketch switches apps, Poketch can be controlled with virtual cursor (L-Stick) or touchscreen.