You may not need an SD. Boot to internal recovery to see what is there. You can either do it with the CM reboot menu or use the key combo. Hold power and n while booting for a few seconds. Release power before it turns itself off followed by releasing n. It should boot to recovery.
If it boots to stock recovery it is easy to get stock back. Just interrupt the boot 8 times in a row by powering off before boot completes. It should then reset to stock.
If it boots to CWM then go to my HD/HD+ CWM thread linked in my signature and download the plain stock zip from item 6. Flash that followed by a factory reset.
Sent from my BN NookHD+ using XDA Premium HD app
See my Nook Color Tips Thread here
and my Nook Color EMMC Partition Repair Thread here
and my Nook Color Updated CM SD Installation Instructions here
and my Nook HD/HD+ stock tips thread here
and my Nook HD/HD+ CWM Root Tools thread here
e.mote's Nook HD/HD+ Dummies Guide for installing CM10.1/CM10.2/CM11 here