I'm currently stuck in Lavender Town, with no Poke flute or Ghost scope. I have tried every direction to get back but I can't find one.
To reveal/defeat the Ghost in Lavender Town, you'll need to find the Silph Scope. It can be obtained by defeating Giovanni in the Rocket Hideout.
You'll need to head to Celadon City, which you can reach by leaving Lavender Town via the western path, and using the Underground tunnel before the gates to Saffron City.
As for the hideout itself, I'll leave it up to you to find, but I've put the instructions in the spoiler section below if you get stuck:
- Head to Celadon City Game Corner
- Talk to & defeat the Team Rocket member inspecting the poster on the wall.
- After defeating him, interact with the poster to activate the stairs to the Rocket hideout
I'll add an alternate answer, based on a well-known oversight in the original Game Boy versions of these games.
As pinckerman commented, you probably shouldn't do this your first playthrough, as it skips one dungeon, makes another dungeon annoying, and prevents you from catching any Ghost-types. Although all of these are reversable by just doing the intended route later.
With that disclaimer out of the way:
- Buy a Poké Doll from the Celadon Dept. Store (4F).
- Trek up Pokémon Tower, running from all random encounters with unidentified ghosts.
- At the last staircase leading up to the top floor, there is a scripted encounter with a ghost. If you run from this one, your character will automatically move away from the staircase, so normally this is where the Silph Scope is required.
- Instead, use the Poké Doll during this battle. The battle will end, as if you defeated the ghost.
- Now you can proceed to the top floor and continue the normal game's sequence.
This won't work in the remakes (FireRed, LeafGreen, Let's Go Pikachu, Let's Go Eevee), but the now-unlisted Virtual Console releases are official emulations, so it will work there.