Fire Emblem: Shadow Dragon/Secrets

Secret Shops
To access a secret shop, you need a VIP card, first obtained in Chapter 17 by an enemy bishop that is sitting on the far south-west corner.

Simply stepping on a suspicious square will allow you to enter the secret shop.

The following are the shops and what they sell:

Chapter 17
Right above the throne in the northeast part of the map, there is an indent in the wall. Here is the first one. And here is what they sell:

NOTE: You can only buy the following items three times before they run out of stock

Chapter 21
In the northeast map in the hilly area. There should be a blue, small blob. This is what we are going for.

Note: Like the last shop, you can only buy each item three times.

Chapter 23
Right above the throne, there is a door square that you can stand on.

Again, they only have three in stock

Chapter 24
In the southwest part of the map, in a hilly area similar to Chapter 21. Same blue blur you are looking for.

Note: Again, three max buys only