i've checked a couple places and they can order them in as well. ideally i'd like to be able to see the tile first, but if my only option is to order i'd rather it come to my door. fewer trips out. i'm also concerned that the tiles will be like half an inch too big or too small and i'll have to send them back out again for a refund. either way i'll make it happen, just weighing my options. ;-)
Something that you might consider is heating from above with a CHE (ceramic heat emitter). It will heat the slate below it which will then provide the proper belly heat needed. This is actually much more natural than heating with a uth as it simulates the sun heating the rocks like it would in nature. No matter what you use for heating, it should be used in conjunction with a quality thermostat.