When you first arrive in Fuchsia City, you will find the Safari Zone Warden within his own home. However, he won't be able to speak to you. Believe it or not, this is because he actually lost his false teeth somewhere in the Safari Zone. Of course, it will be up to your trainer to find them for him so he can speak once again.
By making it to Area 4 of the Safari Zone (the further back area within the Safari Zone), you will find a pair of Gold Teeth directly outside the Area 4 House where you will receive HM Surf as a prize. By bringin these Gold Teeth to the Safari Zone Warden, he will be able to speak once again. After he can, he'll be gratious enough to teach your player HM Strength as a reward.