Of course the best option is to buy in a Tibia Store your own Hireling with ability to sell magic stuff. You need also to buy a house which is near to your favourite hunting place. So it's an expensive solution.
One of not many NPCs who sells every kind of runes/potions is , however this NPC is far away from everywhere, maybe except Deeplings, Deathlings and The Hive. Unfortunately I barely visit him because of his location.
Same with Ghorza , you can find him on Krailos.
On Feyrist you can meet with Talila or Validara , depends on time in Tibia, both have full offer of runes and potions.
As you can see all of them are in places, that are not very popular, and location may be a problem... so if you need everything at once I suggest you to forget about "perfect" NPC with everything in his offer and visit places where you can find 2 NPCs in the same place.
Most often I visit Rathleton NPCs - and , first one offers all kind of runes you need and the second one - all kind of potions. As you can see, there is no perfect NPC, but both are in the same building so it's really not a problem if you are hurry. Also Oramond has a nice connection with other cities.
Another pretty useful place to refil is Issavi market, which you can find in the middle of city, south from the depo. Here situation is the same as in Rathleton - 2 NPCs next to each other with full offer of runes and potions .