There is just one way to have search enabled in Mapsource, use an original Mapsource installation.
from a post on Gpspassion by GmapTool author:
Address search in Mapsource is organised differently then in gmapsupp.img. GMapTool doesn't convert index files for address search and you loose that funcionality.
Converting with Gmaptool a gmapsupp.img to Mapsource version it wont support address search.
Index file in Mapsource usually is named *_mdr.img. You can add it to gmapsupp.img, but it won't work in GPSr. Index file in Mapsource is bigger then index used in GPSr, this explains why you get bigger gmapsupp.img. Since GMapTool doesn't convert index files, it can create gmapsupp.img much faster then Mapsource.