A louer signs/quick rental

Where can I get the black & orange 'A louer' signs that people use to rent out their apartments? Also, does anyone have tips about the quickest way to successfully find a new tenant to replace me on the lease?

I have a standard lease contract which I may want to break for a new job outside Brussels. I could either give 3 months notice and pay one month's rent as a penalty, or (I'm told) find a replacement tenant, and get them to take the flat instead. I'm keen to do this as it would save me money. Has anyone successfully rented out their flat: any tips about email lists, websites etc that work well? It's a nice one-bedroom in Ixelles.

Many thanks!