I don't think you need ruby at all. All you need is national dex andtalk to the little girl in sandgem town. Eventually she will say that there are lots of beldum in the desert between stark mountain and the peaceful place (i think its the relax area?) You should catch one on about lv 52
It is a swarming Pokemon. After getting the national dex, you have to talk to Dawn's sister each day until she says there are beldum.
you find BELDUM at rout 210 i think. its somewhere in a desert area.
you can catch beldum at route 228 with poke'radar
if you wanna catch beldum it a mass outbreak on route 228
You can catch one in route 209 and route 214 if you have Pokemon leafgreen inserted in the gba slot of your DS.
Pokemon like Anorith, Lileep, Beldum, those kind.
check in the pokedex
Steven Stone will give you a Beldum in exchange for a Forretress.
You have to evolve your metacross who is the evolved form of beldum.
u have to have fire red inserted in the gba slot that's how i caught it
You get Beldum for free, from Steven after you finish the Pokemon League, go to Stevens house and the ball will be on the table.
You cannot catch Beldum in Pokemon HeartGold. However, you can trade for it. After you have gone to Silph Co. and met Steven to get your Hoenn starter Pokemon, you can go back after a little bit to find him again, and he will give you a Beldum if you trade him a Forretress.