There are 107 gen 4 Pokemon, not 100. Without trading, you can see every gen 4 Pokemon. (except Regigigas, Phione, Darkrai, Shaymin, and Arceus, which are not in the Sinnoh Pokedex) You can't obtain 2 of the 3 starters, 1 of the 2 fossils, Mismagius, Honchkrow, Glameow, Stunky, Spiritomb, Rhyperior, Electivire, Magmortar, Porygon-Z, and Dusknoir. This means you can obtain 87 gen 4 Pokemon and cannot obtain 20 of them.
Also you should comment when you reply to someone else's comment.