there's a TMFalse Swipe in the route 45 side of Dark Cave. Teach it to Pokemon with CLAWS. Like Scyther and Parasect.
In Soul Silver you don't need to teach it to Scyther because it will learn it at level 13. Catch one in the National Park but only during Bug Catching Contest.
All these Pokemon can learn it, you just have to catch them somewhere or trade for them:
Farfetch'd (level 45)
Cubone (level 27)
Marowak (level 27)
Scyther (level 13)
Scizor (level 13)
Grovyle (level 53)
Sceptile (level 59)
Nincada (level 25)
Zangoose (level 44)
Gallade (level 45)
You can also catch a Sneasel in Mt. Silver and teach it false swipe.
If you look for Pokemon in GTS (Global Trade Station) you will certainly get one that knows it, or can learn it: http://www.pokemon-gts.net/