We have never had any luck getting good quality tires in third world countries anyway, so I'm not sure it's really that much of an issue. We are getting ready to ride from Alaska to Argentina and I'm using 700c tires this trip. We figure we will have replacements sent to us from the USA when we need them.
that being said, we've cycled in lots of countries and have always used 26" before - and couldn't find decent quality stuff anywhere. Even when we used the 26" we either brought spares with us or had them sent. I'm not sure there will be that much difference between 26" and 700c. That's what I say now - ask me in a year or two and I might have a totally different answer!!