It’s tricky to find multiple official sources with pronunciations, since the anime is one of the only sources with voice acting. However, there are many Pokémon guide books that list pronunciations. I happen to own two copies of the Pokémon Deluxe Essential Handbook, which has a pronunciation for every Pokémon prior to Gen VII. Using my handbook and the Internet, here are all the ones I’ve found so far:
Pidgeot: PID-jē-ät in the anime, PID-jit in Pokédex 3D Pro
Rattata: RA-ta-ta in the anime, ruh-TA-tuh in Pokédex 3D Pro and the PDEH
Ponyta: PŌ-nē-tä in the anime, po-NĒ-tuh in P3DP and the PDEH
Gardevoir: GÄR-de-vwôr in the anime, P3DP, and Smash Bros., “GAR-dee-vwar” in the PDEH
Regice: re-jē-AIS in the anime, “rej-ICE” in the PDEH
Kyogre: kē-Ō-grē in the anime, kī-Ō-gər in P3DP (and I think some commercials I saw as a child?)
Groudon: GRŪ-dən in the anime, GROU-dän in P3DP (I also remember this from a commercial)
Deoxys: dē-ŌK-sis in the anime, dē-ÄK-sis in P3DP
Arceus: ÄR-sē-əs in the anime, ÄR-kē-əs later in the anime (they changed it when they realized the original sounded like a British curse word)
Mienfoo: mē-yen-FŪ in the anime, MĒN-fū in P3DP, “MEEN-FOO” in the PDEH
Mienshao: mē-yen-SHOU in the anime, mēn-SHOU in P3DP, “MEEN-SHOW” in the PDEH
And a bonus…
Kanto: KAN-tō in the anime, KÄN-tō in Pokémon Masters (according to Misty, who calls it KAN-tō in the anime!)
This definitely isn’t all of them, so I’ll add more later.