Philmasterplus'
item_search.ash makes this pretty easy. Check out the thread for more technical details.
For Mr Store items, I made this little script for you. It doesn't directly use item_search.ash though - all you need to do is download PUtils.ash from that thread as well as
ZLib.ash, and place them in Mafia's /script folder.
This little script will simply use Philmasterplus' "rare_items" data file, refresh the prices of all the IoTMs if they are more than a day old, print them in the gCLI, and create a data file called iotm_prices.txt in your /data folder with the results. I went ahead and updated the "rare_items" data file with the last few months' IoTMs.
I didn't really know what you wanted to do with them, so you can go from there, although keep in mind that Mafia's
mall_price() function will only return the price of the 5th item, which can be quite different from the price of the cheapest item in the case of rare IoTMs.