It is after Azealea town, towards the west.
You can also head down south from Goldenrod City to get ot the Ilex Forest.
Celebi is the protector of the Ilex Forest.
There is it is in ilex forest
A man in Ilex Forest
A man in Ilex forest will teach your Pokemon the move
Ilex Forest in not in Firered. Ilex Forest is located in Johto. It can only be reached in Gen II or in the unreleased Heartgold and SOulsilver in Gen. IV.
Budew can be found in Ilex Forest and Viridian Forest.
Between Azalea Town and Goldenrod City.
A special event in ilex forest
There is a Move Tutor in Ilex Forest that teaches Headbutt.
It is a wifi event and has past.
there is a man in the Ilex Forest that will teach headbutt to as many Pokemon as you want
you get it in ilex forest after you get your 2 badge! hope this helps