Metagross in Pokémon Soul Silver

Yes, there is, but you're probably not going to like the alternatives. You have 3 choices.

1. You can trade a Forretress to Steven in the Silph Co. (Saffron City) to get a Beldum.
2. You can find Beldum in "Winner's Path" on your PokeWalker.
3. You can find Beldum in the Safari Zone if you have a Forest area with 63 rock objects in it. Or, to find Metang, you can go to a Mountain area in Safari Zone with 56 rock objects in it.

The only way to get Metagross is to evolve from Beldum or Metang.

Note that all of these options require that you've defeated the Elite Four first. There is no way to use a Metagross, even including trading, before you've defeated the Elite Four and gotten the National Dex.