It's impossible to get a legal copy of the game.

would be great if they release it here

Unfortunately, SWAT 4 is a game that will probably be annihilated by the legal mess it is in. Nobody knows who owns which piece of the whole among licences, intellectual property and whatnot, and I doubt the parties involved will even think about renouncing to their potential rights "just" to preserve a classic.
You've got to love Capitalism! What kind of world will this be without some hungry bastards pushing their own creations to oblivion rather than share something? Better gaining nothing and let a great game die than allow anyone else to profit, right? :P
More seriously, that is a real modern plague that threatens art -of any kind- like nothing else, imo.

By the way, I have been very lucky: just two months ago, I found brand new (well, more like "not yet used or opened", since thay have been produced years ago) physical copies of both the original game and the expansion for 2,99€ and 4,99€ respectively, the last in stock. What a deal!

What legal mess? Doesn't it belong to Activision, just like the other three SWAT games?

Sierra was merged with Activision, you know.

Yeah but Swat 4 had 2 publishers - Sierra + Vivendi Universal.

Both were merged with Activision.

As long as it's not as difficult as SWAT3. That last airport level is impossible! Even Rainbow 6 is easier!

Vivendi is not part of Activision Blizzard since 2014 when it split with Blizzard. There is a lot of shares shuffling going on since then. Eitherway only Activision knows who owns the license at this point.

Vivendi Games which was merged with Activision is no more and all the games that they used to publish are now published by Activision-Blizzard. The Vivendi you are talking about is the parent company.

Why is it that when I need an information I always had right under my nose, I suddenly cant' find it anymore? :/
I will link you this article, the best I have found about the topic. I'm sorry I can't give you anything a bit more solid right now; if I'll find what I was searching for, I'll let you know.

i own swat 4 + expansion. game is soo awesome. split teams. although lan wasn't very good. you can't have gold commanding red and blue players like in single player. but awesome game

Yes, I'm aware of this article, but it isn't particularly specific. For all we know, maybe Activision doesn't even want to bother with it; it wouldn't really surprise me.