Yes, for the most part you will be starting over.
Commercial shops generally aren't in expansion mode right now, but here's a list of some names:
NAI
Colliers
Grubb & Ellis
CBRE
Coldwell Banker Commercial
Sperry Van Ness
Keep in mind, some commercial firms will want you to focus on either investment sales or leasing but not both. It will depend on the size of your market too.