In Normal difficulty I was able to buy elixirs from Akara and Pepin but in Hell Difficulty (I skipped Nightmare) they are not selling them anymore. Will they at some point? When? I have nothing else to spend my gold on other then repairs.

I assume you are playing single player, since Pepin does not sell elixirs in multiplayer. According to Jarulf's Guide section 3.2.2 (Potions and elixirs), page 20:

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In multi player elixirs can be bought from Adria once your character reaches level 26. In single player they can be bought from both Adria and Pepin once you have been on dlvl 13 or in the Hive or the Crypt in Hellfire.
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It is silent on whether this is reset on starting a new game, but that seems likely.

I forgot about Jarulf's guide. I actually have the online version bookmarked. I just didn't think to check it.

And yes, all I had to do was enter the appropriate dungeon level, leave again, and now I can get Elixirs. Thank you.