You can't, elekid is found at the valley windworks but only if you have Fire Red inserted in the GBA slot. Meaning since you have a DSi you cannot insert FR into the GBA slot because there isn't one there.
I still have an old DS lite around just to have an extra for trading and things like that. I have a newer one but I kept my old one, didn't trade it in. The older models do come in handy when playing the DS pokemon games.