How to find Suicune in Pokemon Fire Red?

I've read through tons of questions/answers about this, and tried the suggestions. Yes, I started with Charmander. Yes, I've beaten the Elite Four. And yes, I have the National Pokedex. I read that using max repels with a starter Pokemon under level 40 but above the level of Pokemon in the grass that I am searching in supposedly works. However, I've used about 50 max repels on Route 11 with a Lv32 Lapras. After the repel wears off, I go into Diglett's Cave, come back out, spray on repel, try again...and nothing. It's really starting to frustrate me. What else could I do to find Suicune?