Most are hard pressed to find more than a basic factory load at more than one local retailer and a constant supply of them is not likely. You can find them just before hunting season opens or if the retailer will special stock them. The shot size selection is very poor in most areas. If you had to just shoot what is on the shelf the 16 would die again to all but the most die hard shooters. Too easy to find 12 or 20 shells to do the same job.
The internet has saved the 16 in many ways. Now if you are on the internet the 16 ga. world is another matter. You can find wads to load everything from 3/4 - 1 1/8 ounces. Hulls to reload can be found. If you go to the 16Ga. web site they can share information that is literally a lifetime of learning. Loads, advice, you name and they will share it. One person even designed and created his own wad to make a light load easier. Many are shot at clay targets and it makes a very pleasant light load. A Mec 600 Jr. and you are in business. Just like being 16 years old again except you have to pay the bill now. Almost like the good old days.