Stuck on 8th gym

After versing Clair, I see that my pokemon are severely under leveled.
Where is the fastest and easiest place to train them?
My team is:

Heracross Lv. 32
Brick Break
Aerial Ace
Horn Attack
Shadow Claw

Scyther Lv. 32
U-turn
Slash
Pursuit
Wing Attack

Feraligatr Lv. 32
Avalanche
Headbutt
Waterfall
Crunch

Ampharos Lv. 38
ThunderPunch
Charge Beam
Discharge
Thunder Wave

Growlithe Lv. 31
Iron Tail
Fire Fang
Reversal
Take Down

Best place to train them will be at grass Under Safari Zone. Train till lvl 40 there

The grass near the safari zone should help. Also just as a side note for helping you beat Claire your Ampharos has a terrible move set and if you can you should consider evolving Scyther for the resistance to dragon types its steel typing will give it.

Yeah, as the two above said the grass close to the Safari Zone provides a nice spot to train, iirc it's the most common training ground when grinding for Clair. I recommend you keep the moves you have for your team since it's pretty balanced.

I agree with these guys, evolve Scizor and give a few touch-ups to Ampharos' moveset cos it has an all Electric moveset.

Best place to train would be in the patch of grass near the Safari Zone gate.

Also, for Feraligatr, Ice Fang is a better option over Avalanche cos unlike the latter, it doesn't have decreased priority.

For Ampharos, ThunderPunch should be replaced by like, Signal Beam not only cos it needs a little diversity but its Special Attack is higher than Attack.

And also evolve your Growlithe into Arcanine with a Fire Stone cos the higher stats make the difference.