In Gritty mix, turface and granite are not interchangeable. You can substitute perlite or vermiculite for turface. You cannot substitute it for granite! It does not have to be granite. Granite has no special property that it cannot be substituted. Granite was chosen because it can be sourced as a graded product cheaply in large quantities.
Turface is calcinated clay maybe you can find that. Irrigation supply houses are where I get it (used on baseball diamonds in the US, probably track and field as well).
The pine bark is for shifting pH and some water retention.
The turface is for buffering the retained water, same property as perlite or vermiculite; again turface was very likely chosen because of price and available volume.
The granite is for aeration, as in not retaining water. A common replacement for granite is chicken grit (different sizes, get "growers grit"). It can be any kind of inorganic rock, less surface area the better (as in smooth and not porous), round is the perfect shape but not mandatory.
If you have access to a material that has limited water retention, you could substitute both granite and turface for a single ingredient (don't know what that would be).
The final ultra important factor of all three ingredients is particle size. If all three of these ingredients are dust, then you would have muck. If all three the ingredient are giant chunks the roots will dry out. Between 1/4 and 1/8 inch particle size is what you want, it allows breathing while keeping the roots moist. Don't use fine sand, way too much water retention. Smaller particles have more surface area than big particles in the same volume, sounds kinda counter-intuitive but its true. Particle size is all about getting rid of the perched water table, the number one killer of potted plants.
I prefer vermiculite to perlite. Perlite floats to the top, it is a porous rock. Vermiculite expands and contracts like a sponge, so it can reduce compaction, and it does not float. Overall the differences are minor.
A word of warning, dry gritty mix is by far the easiest to work with (it doesn't stick together) but dry gritty mix is very very drying, I'm certain that I have damaged trees because I wasn't right there with water soon as it went in the pot and I fried rootlets by drying them out. Bare rooting is stressful enough on the tree. Just be slow and meticulous when bare rooting and keep them wet as you go.
Gypsum is optional, actually I can argue against using it.