Can you catch yanma in Pokemon silver?

Yea, you can. They appear on Route 35, though there's only a 1% chance of finding them. If you wanna find them faster, listen to the Pokemon Radio program every day until Mary tells you that there's a swarm of Yanma in Route 35. It's easier with the Pokemon Radio thing because the chances of encountering Yanma increase from 1% t0 40%