how do I find the broker for a sold property?

Look at the sign on the lawn for the contact info of the listing broker OR if it was just recently sold, then try looking up the listing online on mls and finding the contact info OR just go to any agent to look up the sold info for you.

You can visit www.realtor.ca and search for the home's listing details. Otherwise like Eugene mentioned, you can check the sign on the lawn, or ask a local real estate agent about the specific property.

You Can contact your Realtor for help.

My first question back would be: are you looking for the listing brokerage, or the buying brokerage? They're usually two different ones, although obviously not always. If it's the listing - well the yard sign should tell you, but on the buying side: contact the listing agent or brokerage, or better yet, ask the realtor you like to use for real estate. That's what we're here for.