On the MAC:
To find out the stores of an item, you can either use the Search by Store in the actual MAC, and go through store name by store name looking for the item's photo OR go the the "items.txt" file in the MAC folder, and use ctrl+F (or Command+F on a Macintosh) and type in the item name. The store names are abbreviated, and if you want, I can PM you the abbreviations, and you can learn from there. (just added a bit more to what Jeanie said)
All the items are not in the MAC, this is true, but it's currently being updated by Blair Rose.
She is going as fast as she can, but she is currently learning java.
To add items yourself check out
this post. The only hard part is some of the coding, which Donna kindly explained for me when I first learned
here.
PM me with any more questions.