Go to Ruin Valley on 6 Island - When you get to the grassy portion, head south. Push the rocks near the southern bend to get the Sun Stone.
Read more: http://wiki.answers.com/How_do_you_get_a_sun_stone_in_Pokemon_fire_red_version#ixzz1NgDWNmox
use a sun stone on a gloom
Obtaining bellossom has not changed in FireRed, you still get them by using a Sun Stone on a Gloom.
SUNKErn SUNKErn SUNKErn
use a sun stone
Get a gloom and give it a sun stone
It should be somewhere around MT Ember.
Go into Ruin Valley on 6 island and go down. The item that is protected by the boulders is the sun stone.
Have ruby or emerald or another sapphire trade you a Pokemon holding the sun stone they received or get one from firered or leafgreen.
There is no dawn stone in Firered.
The sun stone is an item similar to the thunder stone, water stone, fire stone and leaf stone it evolves two pokemon: Gloom and Sunkern.
You get it in island six's Ruin Valley. You must use strength to get it.
It evolves gloom into bellosom. Then it also evolves Sunkern into Sunflora.