Once William the Bastard became ruler of the country, he immediately used his "Executive Orders" to start limiting the importation of weapons and ammunition. The two Bush Presidents were not very pro 2nd amendment and George I was actually anti NRA, though George II was less so. At about the same time, stocks of the old weapons overseas began to run out. Today, you really only find the Mosin Nagant rifles in any quantity and even they are overpriced.
The best place to find the old guns now is pawn shops and gun shows. These are still perfectly viable weapons, as they were when they were general issue to the most powerful armies on earth. I own some modern guns, but I really rely on weapons of this type.
Here are a few of the most common rifles available today.
The Model 1898 Mauser. This is the rifle that most soldiers of the German Army were equipped with at the start of World War I. It's got a very complicated sight, and the rifle is long. At the time, they were concerned about being outreached by French bayonets. Chambered in 8mm Mauser, this is a good shooter and a beautiful piece of craftsmanship. One good thing about the old guns is that they were built to last by people who took great pride in their work.
The Mauser 98K is the German infantry rifle of the 2nd World War. It's a refined version of the Model 1898. The rifle is shorter, the sight is simplified. These are fine rifles. The 8mm Mauser cartridge is full powered, the action is very smooth, and the rifle is superbly accurate.
The Lee Enfield MK.III holds ten rounds of .303 British. This rifle is generally acknowledged to have the slickest action of the class, and someone who has been trained on the rifle can generate a rate of fire as high as 15 rounds a minute of aimed fire. The "aimed fire" is important, because you really can't "spray and pray" with these guns. They have to be used as they were intended. The MK.III was the British infantry rifle of World War I.
The Lee Enfield No. IV MK1 was the standard British infantry rifle of World War II. It is really an MKIII which has been redesigned to require less machining, use more stamped parts, and be produced more rapidly than was possible with the MK. III. Despite all the short cuts, it is a good rifle and was general issue in the British Army until 1956.
The British Jungle Carbine, or Enfield V, is expensive and hard to find. It's a nice little rifle, but the recoil is fierce. It is for very close in work, so the extremely fine machined sights on the gun don't make a lot of sense. The rubber butt pads have all harded in the 50 or so years since these guns were built. The Jungle Carbine is the only rifle I ever fired that gave me a nose bleed from recoil. It uses the .303 British round, and in that light little frame your body absorbs all the recoil. Most people who own these don't shoot them anymore because they are too valuable as collectors items.
This is the Enfield No.IV, MK II. Only a very limited number were made after World War II, and the number imported into the U.S. was tiny. The MK. II is essentially a Number I that has been redesigned to eliminate some of the flaws the Number I had. It's a fine rifle. Most of the one's that came into the U.S. were never issued, so they are just like the day they left the factory.
Collecting these guns used to be a big hobby. But now, with fewer guns in the country, none to be found overseas, and more government restrictions it's mainly older men who still pursue it. The best surplus guns magazine, Surplus Firearms, just printed their goodbye edition. The editor said there wasn't enough interest in the hobby anymore to justify publishing the magazine. Another publisher bought the magazine rights and plans to continue publishing, but it's a sign of the times.
I'll keep on collecting because I enjoy it. There are still gun shows and pawn shops, so from time to time I may find something to add to the guns I already have.
This post didn't address all the rifles out there, and didn't look at pistols at all. I'll try to do that on a follow up.