With all the Montana cards I've gone through over the last year or so I was able to put together this reference list that shows what casino each barcode prefix was used at. There is some slight overlap and there may be some exceptions but it seems to be fairly accurate from what I can tell. Hopefully this might be of some help.

The list is in an Excel spreadsheet that is available on my website's Montana Slot Card Page (the link is near the top of the page)

Check it out at: www.slotcardtrader.com/montana.htm