Where do I find TM Sunny Day in HeartGold/SoulSilver?

Question

I got a lvl 5 Bulbasaur and it knows Solarbeam but I (you guessed it!) don't want the charging turn.

Answer 1

Non-repeatable
- Goldenrod Radio Tower (From a woman on 3F after defeating Team Rocket)

Repeatable
- Rare reward from the Blue Lake Pokewalker course (requires Pokewalker peripheral)

TM011 (Bulbapedia)

Answer 2

here

the girl is giving you the TM 11 sunny day

go in 7:50 in the video