Short answer: Any SD resp. microSD card is required to operate at 3.3 volt signalling in addition to 1.8 volt so any card should actually work.
Explanation: Any SD resp. microSD card will start to operate using 3.3 volt signalling. Only after successful negotiation of both the card and the controller both allowing for 1.8 volt operation will the card and controller switch to 1.8 volt signalling. Currently only a few of our modules (Apalis T30 starting from V1.1A, Colibri iMX7 and the upcoming Apalis TK1) do allow for such switching plus none of our current carrier boards is truly compliant to this due to the MMC/SD card pins being pulled up to 3.3 volts. That said we have not actually noticed this to be any issue and things should usually run just fine.