I don't know about international shipping, but you might be able to send it down here to a gunsmith in the US to build for you.
On the GAP website, the Non typical is listed with a short action and its caliber is listed as short standard and short mags. That means no 7mm Remington Mag or .300 Win Mag version is available. There are 7mm and .30 caliber short mags out there, but from what I've heard of them, they do not handle heavy bullets very well, which limits their effectiveness at long range. also, the barrel looks to be a somewhat light contour for long range shooting. My personal choice for a caliber would be either a 7mm Rem mag or 7mm weatherby mag. In the Hornady Handbook of Cartridge Reloading (8th edition)
, The Weatherby has a 200 fps advantage in muzzle velocity for the same amount of powder than the Remington. Looking at the cases firsthand, the case capacity looks essentially the same, but the bullet's bearing surface on the case is absolutely humongous on the weatherby due to its double-radiused neck, a feature all weatherby calibers have. In theory, this could increase the chamber pressures and put more force on the projectile while it is in the chamber and not yet contacting the rifling. This is my only explanation for the 200 fps jump in velocity. so, a weatherby mag with a 175gr bullet will hit a muzzle velocity of 3100 fps according to the handbook
for the same amount of powder as the Remington Magnum. If you want to start handloading, this performance increase might be something you want to look into. I'll leave it up to you to decide if the performance jump is worth the cost and availability of quality components. Also, the weatherby and remington mags, since they use almost the same powder charge will theoretically have the same barrel wear, which will be reasonable for a magnum, another important thing to consider. Another thing to mention is that, if you ever feel that handloading is too troublesome or time-consuming, the factory ammo availability of the weatherby is virtually nothing. a 7mm Rem Mag might be better for you in this eventuality.
The problem with the .300 Winchester Magnum is that the bearing surface that it has on the bullet is detrimentally short, limiting the weight of bullet that the cartridge can handle. a 200 grain bullet is generally accepted to be the ceiling of the win mag. A Sierra 7mm 180gr BTHP matchking has a higher Ballistic Coefficient than the 200gr .30 caliber matchking, and will retain its velocity better, buck wind better and have higher sectional density than said .30 caliber. The problem with going up the scale for .30 calibers is the recoil generated by shooting a 220 or 240gr bullet at 2900-3000 fps, and the availability of these heavier .30 caliber bullets.
In a custom rifle with a barrel twist rate that can stabilize the 7mm's, I think that they have more than enough long range capability for 1000 yards and beyond. They have a flatter trajectory, lower recoil, higher BC's, and low enough meat damage at close range to be effective in a hunting role at short ranges as well. They are overall, perfect for the kind of shooting I do.
If you put a muzzle brake on it, I would personally go with an American Precision Arms Fat Bastard Muzzle Brake (see link below).
American Precision Arms
This thing was designed with calibers up to the .338 Lapua in mind. I think it will do the best job of reducing recoil on the market at this point, without being ridiculously huge and cumbersome. Do of course get it professionally installed, either while the rifle's at GAP or afterwards once you find a good smith.
I would definitely get the barrel fluted. It will reduce weight slightly without reducing barrel rigidity, or adversely affecting harmonics, and cool the barrel faster in between shots. I don't see any reason not to get the barrel fluted.
Also worth mentioning is stock choice concerning these calibers. The 7mm Weatherby and Remington Magnums will fit into virtually any stock or trigger guard that has a 300 win mag length feeding system, according to some experts I've consulted on the matter, when I was outlining the plan I had for my next custom rifle and asking their advice (surprise! it's going to be a 7mm Weatherby).
Sorry for the rant(s)...