Pro-tip:
Don't purify one by one, purify in bulk.
The way to do this is (and you can theoretically get them all in one go [meaning only needing 13 lvl 3 weapons]):
Save your game before purifying, check what weapons you get and the order you get them when you and your pawn are both on a red vocation, godsbane yourself afterwards, now check the weapons and order for the yellow vocations, godsbane and, you guessed it, check the weapons and order for the blue vocation.
There will be a lot of doubles and some will overlap.
Mark which position the weapons you want for each color are in and purify them in that order, for instance:
1st-4th you purify as red vocations, 5th you purify as blues, 6th-7th as yellows, 8th as red and so on untill you have all the weapons.
The reason you should do it like this is because the game follows a script that dictates what weapons you can get for each individual item and that script resets to a random position once you purify your last lvl3 weapon.
If you don't have enough lvl 3 weapons keep at least one so that the scrip doesn't reset but you will need more if you do it in turns than if you do it in one go.
There's another way to do it and this one is only prefered if you're looking for a specific weapon:
Make sure you have equal numbers lvl 2 and lvl 3 weapons, then check the results for the lvl 2s. If the weapon you want is amongst them then purify the lvl2s and lvl 3s together until the position of the weapon you want.
(if you want a magick bow and it was the 5th position out of 8 lvl 2 weapons as blue vocations then purify 5 lvl 2s and 5 lvl 3s together)
The reason why this works is because the game has another script that ties the results of puifications of the same kind across the levels (1 and 2, 2 and 3)
If the weapon you wanted wasn't between the level 2s you might want to consider purifying all of the level 2s and reseting the the order for those.
Edit:
And for your farming woes you can also godsbane yourself on certain key chests for lvl 2/3 armor/weapons and RC.
