Hi Gary,
I'm glad to help here! The GCT tank will work with both the VCT A1 and the VCT X2 replacement coils, but they will not allow you to use the temperature control feature. The VCT Pro replacement coils will not work with the GCT tank. I'm posting the links to the A1 and X2 replacement coils below.
http://www.smoktek.com/Smok-VCT-A1-Adjustable-Sub-Ohm-Coil-Replacement-Head_p_1285.html
http://www.smoktek.com/Smok-VCT-X2-Sub-Ohm-Dual-Coil-Replacement-Head_p_1287.html
Best regards,
Brad