its at a place called I.P.P. (not joking)there is a pokeball take it. If there is than tell me where it is i checked on the internet and there's no such thing as I.P.P. you actually get it in the Pokemon mansion in cinabar island
you take it to cinabar island by surfing from the Pokemon place in the viridian forest if you have 4 Pokemon badges. but i don't know how to learn surf..... do you? when you take the amber to cinabar island you can take it to a lab and then leave then you will get an aerodactyl.