Where can I find Swecon in the Soul Silver game on my Nintendo DS?

If you mean the aurora Pokemon suicune, you will eventually find it by the house where bill previously lived (a.k.a. The house of the old man when you show him certain Pokemon, he gives you stones). He will be quite difficult to catch without action replay.

You find him at cinabon island then inbetween icrek city and the ninja town and then you go to vermilion city over by the dock and then you go to fusa city then go over by the power things whitch is to the right and then I forget the next part but after that go to the city where mistys gym is them go up over the bridge and go right up the hill hope most of this helps

First encounter cianwood city
Second encounter rout 42
Third encounter vermilion city dock
Fourth inbetween rout 13 and 12
The fith escaps my mind
The sixth/final battle is route 25 it's over by cerulean city, hope this will help you and when I remember the fith spot I will put it in ;)

Suicune is seen in the following places and you must follow it if you wish to capture it. First, it will be found in the north of Cianwood City. After you encounter it there, you will shortly find it outside the entrance of Mt. Mortar in Route 42. Once you find it here, it will leave Johto and head to Kanto where you will see it in Vermillion City soon after you arrive. Next you will see it in Route 14 where it will escape for the final time to be found outside Bill's House in Route 25. This is where you battle Suicune