Can I install an App that is not available in my country's iTunes appstore?

A common way to work around the cross-border restrictions of the iTunes store is by using pre-paid iTunes cards. These are often available on eBay and you can redeem them in the iTunes store for the country of origin (assuming you want US items, you need to buy a pre-paid card from the US.)

It is not possible.

The author of the app selects where the app will sell, and would not be available in other countries.

It IS possible. I have done this. I can't imagine why an app developer wouldn't want everyone to buy their app.

This whole situation seems to be born out of some aspect of international distribution rights, it's archaic but can be legitimately navigated.

The way you have to do it is to change your iTunes billing information to use an account that is billed in a country where that app is "available". Then you'll be able to buy that content just fine and your existing content will function fine too. I operated this way for about a year. I had a friend open a bank account and I gave him money through paypal. He then let me use that account for iTunes access. I don't know of an easier way....

cough

There are OTHER ways too, but I'm pretty sure such discourse is not permitted here. And actually, I haven't explored those as I fear big brother will have a temper tantrum.