Your Gardevoir is fairly standard, Will-O-Wisp or Destiny Bond are also options for the last move. You can attach either Leftovers or a Salac Berry, with a Timid personality.
Flygon-Not bad, but realize that by going with a special sweeping Flygon, you are going to be giving up some power from Earthquake, because your EVs are going to have to be used for Special Attack. Earthquake will still be useable, but it just won't be as strong. However, the physical sweeping Flygon will be better with FR/LG, when it can get Rock Slide. Your moveset will work ok, you will probably want to go with a neutral personality though. Attach either Leftovers or a Petaya Berry.
Breloom-Not bad, but be careful, because Sludge Bomb could get in the way of Spore if it poisons the enemy. I would go with Leech Seed instead. Also, instead of Counter, there are a couple of possibilities, such as HP Rock, HP Ghost, Mach Punch, Protect. Also, if this is a 386 online battling team, Swords Dance is another option, as Breloom can get it in Fire Red/Leaf Green. Attach Leftovers, and use an Adamant personality.
Weezing-Good moveset. Attach Leftovers. However, some people prefer Fire Blast over Flamethrower on Weezing, it is less accurate, but more powerful, and it seems to be a popular choice for Weezing, especially if you use the standard Jolly personality, which is +Speed, -Special Attack.
Lanturn-Pretty good!! You might want to get Thunder Wave on the moveset though, since your team doesn't have a paralyzer. You could use T-Wave over Confuse Ray, attach Leftovers, with a Modest personality.
For your last Pokémon, you could use Dusclops, it is not weak to Ground types, and your team isn't all that weak against Earthquake, either. Only Lanturn is weak against Ground, Weezing and Flygon have Levitate, so they are immune to Ground attacks, and Breloom is a Grass type, so Ground types are not very effective against Breloom.
There are a couple of ways that you can use Dusclops.
Calm Mind
Will-o-Wisp
Ice Beam/Psychic
Rest
@Leftovers. (Bold Personality)
or
Night Shade
Mean Look
Will-o-Wisp
Confuse Ray
@Leftovers. (Calm Personality)
or
Will-o-Wisp
Imprison
Night Shade
Rest
@Leftovers. (Calm Personality)
The top set is a tank that can attack after Calm Mind is set up, the middle set is a trapping set, and the last set is a tank stopper, Imprison will prevent the opponent from Resting, and also protects you from Will-o-Wisp.