After you get the National Pokédex, you get access to a wide variety of areas. In these areas you will battle trainers with Pokémon from regions other than Sinnoh, most of whom are actually wild. Below is a partial list of these Pokémon and most of them are wild, and if they themselves aren't, then chances are their pre-evos are somewhere to be found, so be on the look out:

Nat. No. Selection Pic Name Type 1 Type 2
#019 Rattata
#020 Raticate
#021 Spearow
#022 Fearow
#028 Sandslash
#043 Oddish
#044 Gloom
#052 Meowth
#053 Persian
#056 Mankey
#059 Arcanine
#061 Poliwhirl
#069 Bellsprout
#070 Weepinbell
#079 Slowpoke
#080 Slowbro
#083 Farfetch'd
#085 Dodrio
#086 Seel
#097 Hypno
#102 Exeggcute
#105 Marowak
#108 Lickitung
#110 Weezing
#115 Kangaskhan
#117 Seadra
#123 Scyther
#127 Pinsir
#128 Tauros
#131 Lapras
#147 Dratini
#148 Dragonair
#178 Xatu
#180 Flaaffy
#193 Yanma
#206 Dunsparce
#217 Ursaring
#219 Magcargo
#228 Houndour
#232 Donphan
#236 Tyrogue
#241 Miltank
#263 Zigzagoon
#277 Swellow
#281 Kirlia
#286 Breloom
#288 Vigoroth
#294 Loudred
#296 Makuhita
#297 Hariyama
#301 Delcatty
#318 Carvanha
#319 Sharpedo
#323 Camerupt
#328 Trapinch
#329 Vibrava
#332 Cacturne
#333 Swablu
#334 Altaria
#342 Crawdaunt
#344 Claydol
#353 Shuppet
#355 Duskull
#356 Dusclops
#357 Tropius
#364 Sealeo
#370 Luvdisc
#373 Salamence
#376 Metagross