Hello I would like to help you.
I think I will need a little bit more information from you. It is possible to put maps on a external SD card and load them into your GPS. A lot depends on what brand of GPS you have and if the maps were installed on the external in the proper format for your particular GPS.
What kind of GPS do you have?
are the maps supposed to be on the external card that you got?
If there are not already on the card where was your husband supposed to get them from?
He has and Astro 220. The card is balank and he was told we could download the information from the internet.
Okay you can tell your husband that he can go to the Garmin web here https://my.garmin.com/maps/chooseDeviceType.htm?#
And when he gets there it will install a Garmin update application to the computer. And this will allow him to update his device.
Once he has gone to the update procedure as you may get a free upgrade of maps already by doing what I said above. He can then go to this section of the Garmin site to purchase the maps he needs for the area he will be hunting. https://buy.garmin.com/shop/buymaps.do
I hope this helps you. please let me know if I can help you further