I believe saltpeter can be dug up, in the current version.
[MATGLOSS_STONE:SALTPETER]
[NAME:saltpeter][COLOR:6:7:1][TILE:'x']
[ENVIRONMENT:SEDIMENTARY:CLUSTER_SMALL:100]
[SOLID_DENSITY:1201]
On balance, a blunderbuss should really be harder to make than a musket, since the muzzle has to flare out evenly. Even very small inconsistencies will make the accuracy complete and total poop (meaning that 99% of historical blunderbusses had no accuracy to speak of). Even with buckshot, you'd get the absolute worst, doughnut-shaped patterns you've ever seen. You basically wouldn't have much of a chance of hitting past about 10 yards.
Historically speaking, anyway, the giant "pilgrim blunderbuss" you see would not have been at all common. Real blunderbusses were typically carbine-sized or smaller, with about a 12"-18" barrel, and about 2 feet long overall. Mainly used in situations where one would be fighting at very close range and need to reload fast, without standing the weapon up on the ground. One reason why they're heavily associated with naval combat.
On muskets, a good quality smoothbore can actually be quite accurate, and print groups of about 5-6" at 100 yards, with plain round ball. The main issue is that kind of accuracy requires a tight-fitting ball and patch, which would have been used for hunting, but not for warfare. Slower to load, and after about 2 or 3 shots with tight-fitting shot, you wouldn't be able to reload anymore due to powder fouling. So soldiers were typically issued extremely undersized shot that would rattle around on its way out of the barrel.
Early rifles were really only marginally more accurate than a good quality musket with tight-fitting shot, but that actually was not their main advantage. The main advantage was the rifling grooves meant more room for powder fouling to accumulate, which meant you could shoot for an entire battle, without having to switch to undersized shot. Actually, some "transition" muskets used straight grooves for that very purpose, before someone went "hey, if these grooves were a spiral, the shot would spin!"
So basically:
Blunderbuss - light, compact, fastest to load (next to a pistol), effective range 15 yards.
Musket with tight shot - huge, heavy, slow to load, can only manage about 3 shots before switching to loose shot, but effective range is about 120 yards.
Musket with loose shot - same as above, but a little faster to load, and only accurate to maybe 50 yards or less.
Rifle - same enormous size and weight as a musket, much slower to load, but it's accurate out to maybe 150-200 yards all day long.
This reminds me of the time when I tried to do a mod for Mount&Blade, introducing American Civil War era firearms. I basically wanted to reproduce the time in history where horses were still a major contribution to field warfare, and where muzzleloader vs. cartridge arms was still a valid tactical consideration. But technical limitations mean that that's very unlikely to ever happen.