It's the refinement that's the real issue: anyone who's braised a big joint of meat knows that a couple of hours of low-temperature stewing will net you large amounts of gelatin. Hooves and antlers were the preferred media, but anything that's got a bunch of collagen will work. Talk to your butchers shop, and see if you can buy some bones.
Refinement was done the old fashioned way: by hand. You skim the top to remove the scum, you add egg whites to degrease and to clarify the "broth", and then you strain and strain and strain and strain.
And strain. And strain. And strain. The skimming/straining process is similar to rendering sugar from sugar cane, if you've ever done it (slightly less esoteric, because people still like molasses). They obviously don't use egg whites in rendering sugar.
It's a huge amount of work (and OMG it stinks...do it outdoors if possible), and the end result is probably not going to be on par with the stuff you buy from the store. Unless you're hankering to re-invent an ancient technology just for the fun of it, I'd just buy it.
Edit: I dug around, and there are a number of products for straining jelly that might make it easier, and they should be able to deal with the viscosity of the gelatin soup. Unfortunately they seem to be made for smaller batches, and that may not be helpful if you're doing a huge kettle.
Yes! I was able to make a panna cotta using this product in a standard recipe with some minor changes. Just incorporate the Jell Dessert powder where the gelatin is called for and subtract 1/4-cup from the prescribed sugar.
I started with this recipe on JoyofBaking.com.
The recipe, like most I've seen, calls for one standard 1/4-ounce packet of gelatin. From what I've read (e.g. here) this amount is used to gel 2 cups of water in standard application. The preparation directions for the Jell Dessert also call for 2 cups of water, so it probably contains an equivalent amount of gelling power to a standard packet of gelatin.
The main ingredient in the Jell Dessert powder that isn't a gelling agent is sugar. As sugar is also a major ingredient in panna cotta, I figured that I could try cutting the sugar by the sugar content of the Jell Dessert. I estimated this amount by observing that the Jell Dessert is two thirds sugar by weight (14 g of each 21 g serving, according to the Nutrition Facts), measuring the total volume of the powder at a bit more than 1/3-cup, and assuming that all of its ingredients are of similar density. A little more than two thirds of 1/3-cup is 1/4-cup.
So, I made the following substitutions to the standard recipe:
When the recipe calls for sprinkling the gelatin onto cold milk, I instead mixed the Jell Dessert powder with the milk. I mixed instead of just sprinkling because I was afraid that the additional ingredients would clump around the gelling agents and prevent them from getting properly wet, otherwise.
I cut the powdered sugar to cook with the cream from 1/2-cup to 1/4-cup.
The result was, as far as I could tell, a successful, strawberry-flavored panna cotta. I'd never tasted panna cotta before, so I didn't have a basis for comparison, but it set nicely, was pleasantly creamy, didn't taste too sweet to me (at least, as served with semi-sweet chocolate sauce), and was, in my opinion, delicious.
I expect that the same substitutions would work for this product in other panna cotta recipes. I'm not as sure whether other prepared Jell Desserts (including Jell-O) would work the same way or not.
Best Answer
From the National Center for Home Food Preservation:
Making Jelly without Added Pectin
Making Jam without Added Pectin
Fruits low in pectin: apricots, blueberries, cherries, peaches, pears, raspberries, and strawberries. That's not saying you can't make jam/jelly/butter from these without added pectin. It just may be a little more difficult than, say, using apples. In fact, as an example, here's a pear butter recipe w/o pectin.