Certain items are more or less restricted in different countries. Some are more expensive (software in Australia etc.) And some are in less demand so less available.
What is the best and/or simplest way to cover this for other countries?
The simplest way is to rely on your gut instincts and your knowledge of the country in question, make a quick judgement that sustains suspension of disbelief and doesn't bog down the flow of the game. In my opinion, this is also the best way.
However, if you're more crunch-oriented and like your realism, use google (combined with google translate, if needed) to look up stores of the country in question where the item to be purchased is available (or, in case of legally unavailable items, look up the legal stuff about the item), compare it with the default in the nWoD books, take income differences, purchasing power parity, local laws, economy, geographic, social, cultural, legal etc differences...
...but, seriously, I don't think you should do this. Go for keeping up the flow of game. It's Storytelling you're playing, not an economy simulation (I guess.) If you're the ST and the expert on the country in question, make a quick, informed decision. If you're the ST, but a player knows more about the country than you do, ask for their opinion, make a decision, get on with the story. If you're a player, and not an ST, go with what your ST says (perhaps offer an opinion, if asked for, but don't bog down the game.)
Anyhow, always keep in mind that the nWoD is not our world. It's a dark, twisted reflection of our world, where countless factors definitely not present IRL will influence prices, availability, everything. This makes it especially easy to go for and keep up a made up, yet consistent world-view. Do not bog down the game bickering about the availability or price of a gun. Get on with your game.
Mostly ignore it.
Dots in Resources represent not a certain amount of money, but a certain amount of (relative) wealth. So things are more expensive in one country? Okay, that might mean people having enough money to be moderately wealthy (Resources 4) are fewer (or maybe not). But either way, anyone who has moderate wealth can afford roughly the same things everywhere, e.g., a nice car.
This is a generalisation, but as has been said, it's not worth wasting time individually repricing every item.
My exception to this is for thing that are illegal/require permits to own. The Armoury rulebook has section on gun law around the world, which is still appropriate in GMC-RU as it is mostly fluff.
My own ruling is if you want to acquire though legitimate means something that is restricted, such as a gun, you need a merit to represent that.
So, Status 1 Security Guard would represent your being able to carry a handgun of rating up to 2L (In Australia, certain security guards, e.g. if transporting money to/from a ATM, are allowed guns. Most, like bouncers, are not.) Having Status 2 represents that you (or your employer) has convinced the authorities that you need to be armed with a high-classed weapon -- probably a damage 3L handgun. But that status only represents having a licence for that particular class of weapon. (You can look up weapon law for your country.)
It doesn't necessarily have to be status. I would (have) also allow say a few dots in Fame as a Olympic marksman get by.
There are certain restriction on what you can do to not break the rules of your permits.