For DIY "neolube", I see that the solids are 75% graphite and 25% "thermoplastic resin", and that solids make up about 3.3% of real Neolube. So, if trying shellac as a substitute for the resin, then I would start with 1 part shellac flakes to 3 parts graphite, by weight. (Yes, shellac starts as solids (beetle secretions in Thailand) and is sold that way, but I have no idea where or in what quantities.)
Shellac as we know it is those solids dissolved in alcohol. It has a shelf life of about a year, after which it remains tacky when dry. So, it is probably not a great experiment to use some that has been sitting around your shop forever if you intend to put it on a model.
Also, commercial shellac is made with ethyl alcohol. So, I am not confident that using isopropanol works with shellac.
And, shellac is an electrical insulator, so the DYI neolube stuff might or might not be useful on conducting surfaces.
Cans of "liquid" shellac are specified as having shellac solid content in "pound cuts" where 1 pound cut is a pound of shellac solids dissolved in a gallon of ethyl alcohol. I don't have any on hand, but Wiki says hardware stores sell shellac in 3 pound-cut concentrations.
So, it is going to take a bit of math to get something like 0.8% of shellac solids in the DYI neolube if you start with liquid shellac from a hardware store. Ethanol has a density of 6.5 pounds/gallon, so "3 pound cut" shellac should have something like 3 pounds of solids per per gallon (or more, depending on how much volume increase occurs when adding 3 lbs of shellac solids to 1 gallon of ethanol). Let's assume it is close to (3x16=)48 ounces of shellac solids in (3x16 + 6.5x16=) 152 ounces of shellac, which is (48/152=) 32% solids. So, it would need to be dilluted by something like 40:1 to get 0.8% shellac solids by weight in the resulting ethanol solution.
Then, depending on how much of the solution you want to make, calculate the weight of the shellac solids as 0.008 times the weight of the solution and add 3 times that weight of graphite powder.
Frankly, I think it is worth the price of real Neolube just to avoid this effort, and that assumes the resulting solution actually works as well as the commercial product for our purposes. But, if somebody else wants to make the effort, and comes up with an "A$$hatLube' that, upon experimentation works well for us, then I might whip up a batch the next time I buy any shellac.