Wand Core Materials
In my Next-Gen WIP, I'm currently writing the chapter where my main character gets her first wand. I've decided to go with hazel for the wood because of the where her birthday falls on the Celtic wand chart on Jo's website, but I'm struggling with the core. From something on Jo's website, I get the slight impression that Ollivander only uses dragon heartstring, unicorn hair, and phoenix feathers in his wands, but it's just that -- an impression. I could be totally wrong.
Actually, I hope I am wrong. I really want my MC's wand core to be very unique, something Ollivander would comment on. However, I'm having a hard time coming up with the material to match her abilities, which fall under the realm of Divination.
So I have two questions. First, do you know anything definitive about the materials Ollivander uses for wand cores? If not, do you have any ideas for a wand core that would somehow be fitting for a Seer or the like?
Ollivander uses only phoenix feather, unicorn hair, and dragon heartstring. Out of those, unicorn hair seems to me to be the core most suited for a Seer. I don't know why. If you want, since it's a Next-Gen story, you could kill off Ollivander (I'm planning on doing that, myself, in the story I'm working on) and have your OC go to another wandmaker, who would then use something different for the core. It's your story, and therefore your choice.
The problem with a really unique wand core is that is venturing near Mary-Sue territory. Even super-special Harry Potter had a core of Phoenix Feather, and not something really weird like Acromantula fang or ground-up fairies or anything like that. Since you are using Ollivander, you are limited to dragon heartstring, unicorn hairs, and phoenix feathers. Concerning which one would be best for a Seer, I have a feeling it would be unicorn tail hairs, if only because neither bits of dragon or phoenix seem to work in my mind for some reason.
Tim the Enchanter
It is canon fact that Ollivander only uses unicorn hair, dragon heartstring, and phoenix feathers. Maybe what you could do is say that the wood and the core don't usually go together because they are normally not a compatable combination.
While it's semi-canonical that Ollivander only used unicorn hair, dragon heartstring, and phoenix feathers in his wands, I don't think it's impossible that he could have ever created any wand with anything else. He's a wandsmith, and he's pretty old -- it's quite likely that he experimented with numerous materials earlier in life. Perhaps he's gone through phases where he preferred other things, before settling on those three as the ones he likes best. He might also now and then just like to experiment and try something different. So it's not like you're breaking canon if you provide a reasonable explanation for why Ollivander made one wand differently.
Note, however, that Ollivander making a special and unusual wand that then somehow chooses your character will, as Tim mentioned, be veering into Mary Sue territory.
If this is next-gen, though, you could have Ollivander working with an apprentice. (I've seen quite a few fics where he's assumed to be preparing someone else to take over for him, after the war.) Perhaps this apprentice is just starting to get good enough to make his/her own wands that are worthy to sell, and your character receives one of them. Ollivander could comment on it then, especially if the apprentice is experimenting with (or has settled on) a wand core material that Ollivander doesn't use himself. (Possibly he even disapproves.)
A wand that is good for divination? Hmm. How about hair from a centaur's tail? (One wonders how the wandmaker got it -- and it's probably not something your character would want to brag about having, especially in the vicinity of the Forbidden Forest...)
He's also not the only wandmaker in Britain - just supposed to be the best. (I think Lupin says something along these lines in DH) What is possible is that he's not alive anymore. I imagine that the year or two spent being tortured by Voldemort would have left him extremely weak.
Perhaps he has a son or nephew (daughter/niece) who took over the business.
It's too late to kill Ollivander off or at retire him, because he showed up in the last chapter I posted. It's a good point about a very unique wand core being a Mary-Sue trait. I'm afraid she already is a Mary-Sue :(, so I probably don't want to make it any worse. I guess I'll stick with regular old dragon heartstring.
If you want to make the wand special, though, maybe it could seem ordinary in the hands of any other wizard, but be especially powerful in the hands of this one particular girl. If you still want to make the wand somehow special, that is.