You're certainly NOT going to waste a feat slot on a spell if you're a wizard. Any spell. Ever. That sort of stuff is for sorcerers.
What you do is find a caster not hostile to you that knows the spell (the game didn't let you ban Divination; aren't you happy about it now?) and then you're going to bribe the hell out of it to let you copy the spell or help you make a scroll of it (money stopped being an issue at level 11-12, when you became able to cast Wall of Iron and thus gained access to a limitless supply of a valuable trade good).
This gets you, at worst, a scroll of any spell that any bribeable NPC can cast (I say at worst, because some casters don't have spellbooks, and some of those that do will be understandably reluctant to let you handle them). Then you're faced with a Spellcraft DC of 15+spell level (that you're probably not going to fail at low-levels, almost assuredly aren't going to fail at medium-levels, and at high-levels... well...) and then you can copy it into your spellbook.
Now, though it isn't mentioned in the relevant part (i.e., the "adding spells to your spellbook" section), the mention of "arcane spells" can be found peppered about here and there, and your DM might not let this fly (there's a couple of gems in the divine lists that you might make good use of). This just means that your going to aim your spell-knowledgeable-searching divinations at all the lovely, lovely Dragons, Nagas, and Rainbow Servants out there (Nagas and Servants might require a bit of negotiating, but I assure you any true Dragon, a.k.a, the ones you care about, is going to be more than happy to take your money in return for the casting of a spell).