I don't want anyone to explain it. I stated that in the OP.
Well at the moment there is not much literature on the topic....if there were I assure you I'd have it. Anyways Eywa has written many statistical guides on Diablo II and probably wrote half of the literature you've read on Diablo II, I assure you that is the best place to look.
Edit: This is the best I can find. Credits go to Eywa for writting the below.
Relevant id list, as per Skills.txt
66 nec Amplify Damage
67 nec Teeth
68 nec Bone Armor
69 nec Skeleton Mastery
70 nec Raise Skeleton
71 nec Dim Vision
72 nec Weaken
73 nec Poison Dagger
74 nec Corpse Explosion
75 nec Clay Golem
76 nec Iron Maiden
77 nec Terror
78 nec Bone Wall
79 nec Golem Mastery
80 nec Raise Skeletal Mage
81 nec Confuse
82 nec Life Tap
83 nec Poison Explosion
84 nec Bone Spear
85 nec BloodGolem
86 nec Attract
87 nec Decrepify
88 nec Bone Prison
89 nec Summon Resist
90 nec IronGolem
91 nec Lower Resist
92 nec Poison Nova
93 nec Bone Spirit
94 nec FireGolem
95 nec Revive
1) The game chooses how many skills (staffmods) to add, based on a random roll, rnd (returns a random integer, 0-99).
- If 90 or higher (10 %): 3 staffmods
- If 70 or higher (20 %): 2 staffmods
- If 30 or higher (40 %): 1 staffmod
- Below 30 (30 %): no staffmods
2) Next, it selects the skill id (tier), starting at a certain value depending on ilvl:
- ilvl 1-11: ID 1
- ilvl 12-18: ID 2
- ilvl 19-24: ID 3
- ilvl 25-36: ID 4
- ilvl 37+: ID 5
This becomes a base (static value) for all the skill ids on that item. Then it has a chance to be modified (this is done in turn for each staffmod),
- 20% chance of +1
- 50% chance to stay unmodified
- 20% chance of -1
- 10% chance of -2
Starting at each of the base values 1-5, the possible tier spread combinations are then 1-2 (1), 1-3 (2), 1-4 (3), 2-5 (4), and 3-6 (5). In other words, staffmods must fall within a block of 4 adjacent tiers (rows in the skill trees).
SM and RS are tier 1, whereas RSM is tier 3 (reqlvl 12), so we must restrict ourselves to a starting tier of 2 (ilvl 12-18) or 3 (ilvl 19-24) for all three skills to spawn.
If the item is low quality, then the skill id as of now is capped at 4. Then the final id is chosen from the following formula, with skill_adder being the skill id so far (modified or unmodified as above), and base_id is the starting id for the character class, viz, 66 for Necromancer skills,
- id = skill_adder + (base_id + 4 * skill_adder) - 5 + rnd
which may be simplified to: id = 66 + 5 * (skill_adder - 1) + rnd. Since id = 69, 70, 80 are the desired ids, we need skill_adder = 1 on two of three id rolls (to get RS, SM) and skill_adder = 3 to get RSM.
3) Finally, the skill bonus (+1-3) is chosen, again based on a random roll, rnd (returns a random integer, 0-99).
- If 90 or higher (10 %): +3
- If 60 or higher (30 %): +2
- Below 60 (60 %): +1
This is done in turn for each staffmod chosen.
Because we want 2 sockets and ilvl < 25, we are left with just one option: Bone Wand (qlvl 18).
So either find an ilvl < 25 Bone Wand with the desired staffmods or shop for one in Acts 2-5 Normal, using a level 13-19 character.
Voodoo heads must be found, which does complicate matters somewhat.