There are books out that detail how to make suppliments at home. Some I use are brewers yeast and fish oil. I haven’t made ground eggshell yet. Some people even go so far to make their own bonemeal.
I don’t worry about the bonemeal, since I use meat that’s been ground up with bone and most internal organs. Fortunately, I can also get chicken hearts and livers from the same source, so a lot of the nutrients are coming right from the animal source. The glandular supplement and Vit B complex are from who-knows-where. Hopefully the high quality mean/bone/organ meat/egg yolk ingredients make up for any deficiencies in the remaining supplements. It’s got to be more nutritious than a diet of field mice!