I checked online, the only place I found was ParthenonFoods.com
their cheapest package is 1lb (22 slices), for $8 + approx $10 shipping for 2day.
I assume this stuff can freeze ok so I could get a bigger package
5lb (110 slices) $37+$18SH
or uncut 2.5lb $18+$13SH or 5lb $30+$18SH
Add the price of the pita, sauce, etc, its prob a little over $4/gyro. $3/gyro if you got a bigger package. Seems pricey, but prob half the price of what you would get from a restaurant. They probably get their meat from the same place.