However, you can get a Ditto in Soul Silver, which can breed with other Pokemon to get Lapras eggs.
Here's how to get a Ditto and breed a Lapras:
1. Find Ditto: You can find Ditto in the following locations:
* Route 42: After getting the HM01 Cut, you can use it to open a path and access a hidden area with a rare Ditto encounter.
* Lake of Rage: After beating the Elite Four, you can find a Ditto in this location.
2. Obtain a Lapras Egg: You need to trade for a Lapras or find one in a trade. You can also use the Game Corner to get a Lapras egg (but it's very rare).
3. Breed the Lapras: Breed your Ditto with your Lapras to produce Lapras eggs.
4. Hatch the Eggs: Once you hatch the eggs, you'll have your very own Lapras!
Important Notes:
* Breeding requires a Pokemon with the "Everstone" held item. This will ensure that the baby inherits the parent's nature.
* You need to have the "Day Care" feature unlocked to breed your Pokemon. This is available in the Goldenrod City.
While you can't directly catch a Lapras in Soul Silver, this breeding process is your best bet to obtain one!