I think a wand with skeleton mastery and raise skeleton cannot have +3 to summoning. It needs a low item level in order to get bonuses to SM and RS, but a high affix level for +3 to summoning skills. If I remember right, not even the 3 chipped gem recipe can do the trick with an elite wand. That recipe produces ilvl 25 items which is already too high for L1 skills. You can get a rare +5 one, however, by applying the 6 pskulls recipe repeatedly on an elite wand or by getting one imbued by Charsi at a low character level. Even that would need incredibly much luck (and thus incredibly many skulls or quest rewards), like rolling 3 Yahtzees in a row. It still wouldn't necessarily be better than an Arm of King Leoric.
If you want to know more about the affix and item level and related issues (like how the affix level is calculated from the item level and other numbers, how the 6 pskulls recipe works etc.), have a look at the statistics forum.
Arm of King Leoric is the ultimate summon necro wand. Apart from its other bonues, it also gives +2 to all summoning skills as well, so it ends up with +5 to raise skeleton, +5 skeleton mastery - which is probably as good as White's +3 RS and +7 SM. I would just use it for summoning and switch to something else once you have the skeletons, however, even if that means losing a skeleton, because its chance to cast bone prison when struck might entrap you with an enemy.