Wish allows the user to "Duplicate any wizard or sorcerer spell of 8th level or lower, provided the spell is not of a school prohibited to you". Is this enough to give myself, say, contingent True Seeing? I'm trying to give this benefit to a caster who hypothetically knows neither Contingency nor True Seeing .
Yes, it can, and there is no reason whatsoever to think that wish would be required to supply the companion spell—that could just be cast regularly as you cast wish-as-contingency. And if you want to cast wish-as-true seeing as the companion spell, there is also no reason that should fail.
Basically, it works because everything involved says it works, and nothing says it doesn’t. You need two castings of wish, but you can cast wish twice so that’s not a problem.
Trying to get the final contingent true seeing result from a single casting of wish, though, that would be a “greater effect.”
Since Wish only duplicates effects of existing spells, and that Contingency would produce no effects by itself it would fall in the Greater effects category if you don't cast the companion spell yourself or have another Wish mimic the companion spell (Thanks @KRyan)
(...)You may try to use a wish to produce greater effects than these, but doing so is dangerous. (The wish may pervert your intent into a literal but undesirable fulfillment or only a partial fulfillment.)(...)
If you want to go safe Use Magic Device might be your best option, there's always the spell Divine Insight (up to +15 on a single skill check) that could help you with harder UMD rolls. or Greater heroism (+4) if you want to make it cheap depending on your class.
If you're a wizard with prohibited schools, some prestige classes might help you but if the spell is just hard to get, you could craft a scroll with limited wish (if the DM agrees) or even Wish to craft a scroll of a rare spell so you can write it in your spellbook! see My answer and Quadratic Wizard's answer to the question:Can you craft magic items using Wish instead of the required spell? for more info on the mentionned method.
If you're a sorcerer perhaps Knowstones are accessible.
Clerics also have access to domains with those spells but you would cast Miracle instead if you were one without the right domains. Last suggestion, perhaps Miracle (via an ally maybe?) with the very powerful request option could give it to you, might not be possible unless you're the one to cast it, if you use UMD to do so... might as well go with contingency scroll via UMD and True seeing scroll via UMD...