I'm afraid that I don't have any links to sheet music, but I can play some songs on the piano. I can give you the simple melodies (because I can't get the harmonies to line up correctly) and, for most of them, the key.
Challenger!! is in c# minor. I figured out some of it:
f#g#f#g#f#g#f#g#f#g#f#g# g#g#g#g# bbbc#
(Ikukkyanai yarukkyanai makekonai tomaranai saigo made)
f#g#g#f#g#f#g#g#f#g#f#g#g#g# bg#f#ef#f#f#g#f#
(Hitori ja nai samishikunai mada mada waku waku bouken owaranai)
f#g#f#g#f#g#f#g#f#g#f#g# g#g#g#g# bbbc#
(Ikukkyanai yarukkyanai makekonai tomaranai itsudatte)
f#g#g#f#g#f#g#g#f#g#f#g#g# bbg#f#ef#g#e
(Sasaetai mamoritai kimi ga kizutsuita toki wa)
f#g#g#f#g#f#g#g#f#g#f#g#g#f#g# g#g#g#g#g# bbbc#
(Furimukanai utsumukanai hekotarenai akiramenai shinjiteru)
f#g#g#f#g#f#g#g#f#g#f#g#g# bbg#f#g#ef#f#g#e
(Aseranai awatenai itsumo haruka na yume mezashite)
What Kind of Pokémon Are You? is in a minor. Here's the chorus:
aacefefd bbcdededca aaacdcedde
(What Kind of Pokémon Are You? How do you do the things you do~? Share with me your secrets deep insi~de.)
aacefefd bcg(higher)ggae(down) aaabcefa~ ddcdcdc(dca very quickly)
(What Kind of Pokémon Are You? Are you loyal through and through? And do you have a heart that's true~? What Kind of Pokémon Are You~?)
One of my favorite dub openings, This Dream. Another a minor:
(aga) abcbaga bcbabagg aabcbcdc edccddb dddde
((Pokémon!) Every trainer has the choice to listen to the voice inside. I know the battle may be long, winners may have come and gone. I will carry on!)
edcccccc cdddce edcccccccga (ddee)
(Yeah, this dream will last forever! This dream will never die! We will rise to meet the challenge every time! (Every challenge!))
edcccccc cdddce ddefededcdca ddefededcdca (aga)
(Yeah, this dream keeps us together; this shows that you and I will be the best that the world's ever see~n because we always will follow this drea~m! (Pokemon!))
The 3rd Pkmn AG ending, Smile, is in Bb major! Here's the vocal part. Flats would be hard to show, so è=e flat and ß=b flat.:
fffffgfèd dddèdcß ßdccßcdd fffffgfèd dddèdcß ßdccßcßß
(Koraekirezu ni ima nagashita kimi no namida ga hika~tte. Soredemo kawarazu ni kimama na kaze wa mune wo yusaburu yo.)
feeeeffeaaßaed feeeeffèdcßc feeeeffeacß ßcßagf~fféd~ éc)
(Ga-nbarukoto wa taisetsu dakedo shoujiki na kimi no yowasa wo kakusu tame dake ni aru tsuyosa narana~kute ii~ kara.)
fffffgfèd ddèdcß ßdccßcdd fffffgfèd dddèdcß ßdccßcßß
(Ima wa mienakutemo tashika (pronounced here "tashka", only 2 syllables) ni kimi no mune no naka ni aru nanika wo shi-njinuku tsuyosa wa kimi no egao wo ma~tteru.)
The first Pkmn AG end is Sokoni Soraga Arukara. It's in... uh... d of some sort, I think; the flats or sharps keep changing around. X_x:
da(up)agdge(down)c dddc#dea(down)e(up)~f daagagef a#(up)aggfee~d~
(Furimuite gora-n kimi no tsuketa (this "tsu" is spoken, but doesn't get its own note) mi~ chi~ ga.... Kao agete gora-n mirai wo tsukuru~ yo~.)
ddedef# f#af#e~ef#db d~c#de~def# b(up)af#e~f#eb
(Ganbarukoto ni tsukareta~ toki ni wa so~ra wo mi~agete namida wo~ nagasou.)
eeeef#eedc#da(up)~c#(down)db(up)a eeeef#eedc#da(up)aaaagf#ef#
(Hoho naderu kaze ga ki-tto~ iu (pro. "yoo-oo", 2 syll.) kara "Korondemo ii (2 syll.) sa kimi wa kimi ga suteki sa~.")
da(up)agdge(down)c dddc#dea(down)e(up)~f daagagef a#(up)aggfee~d~
(Kizutsukanu mono ni aozora wa~ mie na~i. Mayoiayumutabi inochi wa kaga ya~ku~.)
def~bbff ddda(up)d(down)ddc#d~f#
(Arui~teyukou soko ni sora ga arukara~~.) (Then transpose the chorus up one step.)