This is information for The Burning Crusade, before Blizzard nicked our easy hit talents from the Resto tree. For better info, see Too Many Alts cos it's not that easy any more, unfortunately.
When I signed up to DPS Karazhan, I made sure I sorted out Kam's spell hit so that he would have the best possible chance of hitting bosses. After all, a spell missed is damage lost.
Firstly I took the talents Elemental Precision Rank 3, Totem of Wrath and Nature's Guidance Rank 3. These give a total of +12% to spell hit. According to WoWWiki, a level 70 Shaman starts with an 83% change to hit a level 73 boss mob with spells. Unfortunately a caster always has a 1% chance to miss. Thus the target additional spell hit which needs to be reached for a boss is +16%. Which means, given the talents outlined and a healthy Totem of Wrath, we need an extra 4% spell hit from gear. Again according to WoWWiki, 12.6 hit rating gives 1% spell hit, which means for 4% we need 12.6 * 4 = 50.4 = 51 spell hit to be sure. So to manage this feat in the same way that Kam has:
Get the Netherfury Leggings and put 2 Veiled Flame Spessarites in. Then fill the last slot with whatever you fancy, Kam has a Runed Blood Garnet. Interestingly, instead of the two Spessarites, you could use a Runed Blood Garnet and a Golden Draenite, which would give +6 spell hit and +7 damage. However, the two Spessarites give 2 lots of +3 spell hit and +4 damage which is actually +6 spell hit and +8 damage, one more spell damage than using a Garnet and a Draenite. I think this is the "rounding error" that I've heard our warlocks talk about.
The above items give exactly 51 spell hit rating and one of the socket bonuses are maintained. Once Kam is revered with Sha'tar he could get the spell damage glyph which also comes with +14 spell hit and would be able to re-gem an item to get some extra spell damage.