Cohai: Thank you for all your help. 
 Unlike my last try at the game, 2 years or so ago, the alchemy bug has been fixed and travelling much further afield has found other formulae. Still to find essence of grace, but will keep travelling 
  You'll never buy essog.  
 your "4 formulas" problem is actually a 22 formulas problem, where the sources are selling only the first 22 indexed formulas of the total 66 formulas in the game. This was an error made by the designers- they thought oh there's 22 different kinds of potions, and they sort of forgot that there were 3 entries (25, 35, 45q) associated with each.  
 The remaining 44 recipes you can never buy start at #23 (35q thunderbolt) and end with #66 (45q firewall). Here is the list of potions in their INDEX order. You will only buy Nox through 25q Thunder, 22 recipes.  
 Noxious Aroma 
 Eyeburn 
 Black Cloud 
 Fleadust 
 Eater Water 
 Breath of Death 
 Sunburst 
 Thunderbolt 
 Arabian Fire 
 Stone-tar 
 Deadly Blade 
 Strongedge 
 Greatpower 
 Trueflight 
 Hardarmor 
 Transformation 
 Truesight 
 New-wind 
 Ironarm 
 Quickmove 
 Essence o'Grace 
 Firewall  
 Where to get the other 44 formulas? Only by the option "trading alchemical knowledge and formulas," which can produce a random one.  
 This is not the sort of bug GOG has any responsibility for and could only be fixed by reverse-engineering the game.