I recomend you to serch on the wiki to be sure what you dont have and how or where to get it.
For weapons, shields, talismans and catalysts you just need to know the location or who drops it or who sells it and boss souls too (sif takes 3 NG because you can make the gratshield, gratsword and gratsword cursed).
For magic Griggs is the only one that sells aural decoy and fall control for wich you need 10 int for him to sell you that. I do not recomend buying any more spells because Logan will sell you all of them in dukes archives. Dusk sells some spells too. Ingward sells resist curse. The rest are found in the game like the dark ones that are spread in oolacile. And for pursuers you need to exchange manus soul to snuggly.
For Pyromancy you can buy most of them from laurentius and quelana. To get chaos fireball and firestorm you need 30 humanity in the chaos servant covenant. To get fire tempest you need to have the pyromancy flame to +10 at least for quelana to appear and i think you can kill her and she drops it although you have no need for that because after you kill the bed of caos she will would give it to you. Black flame is in oolacile. For toxic mist you need to have the egg-head and buy it to eingyi.
For miracles you need to do the sigmeyer quest to get emit force. Most of the miracles are sold by reah after you rescue her from tomb of the giants. In the warrior of sunlight covenant (for what you need 25 faith) you get 3, the lightning spear, great lightning spear (you need 10 sunlight medals) and the sunlight spear (for this one you need gwyn's soul). Karmik justice is sold by oswald. For joining the darkmoon covenant and offering 10 souvenirs of reprisal you will get the darkmoon blade miracle. By killing gwyndolin you will get the sunlight blade. By joining the gravelord covenant you will get the gravelord sword dance and by offering 10 eyes of death you will get gravelord gratsword dance.
Hope it helps xD