What pokemon 1-3 generation pokemon can I catch before I get the national dex?

Question

I just want to know what other pokemon I can catch before I get the national dex.

The main ones I want to know are if Elekid and Porygon can be caught before the I get the national dex.

Answer 1

Only Abra/Kadabra, Magikarp/Gyarados, Roselia, Zubat/Golbat/Crobat, Geodude/Graveler/Golem, Onix/Steelix, Machop/Machoke/Machamp, Psyduck/Golduck, Wurmple/Silcoon/Beautifly/Cascoon/Dustox, Heracross, Aipom, Gastly/Haunter, Goldeen/Seaking, Barboach/Whiscash, Chimecho, Meditite/Medicham, Ponyta/Rapidash, Sudowoodo, Mr. Mime, Chansey/Blissey, Cleffa/Clefairy/Clefable, Pichu line, Hoothoot, Snorlax, Unown, Wooper line, Wingull line, Girafarig, Azurill line, Remoraid, Tentacool, Feebas/Milotic, Mantine and Sneasel.

Murkrow (in Diamond only) and Misdreavus in Pearl only.

To answer your other question. You can't get Elekid or Porygon without the National Dex however with Elekid - it only becomes wild in the game if you have "Pokemon Fire Red" and insert it into the 2nd slot.