Account that import listings from PMW / FreeRentalSite can (and should) add schedule-a-showing functionality directly to their PMW / FreeRentalSite pages.
To do this, contact PMW / FreeRentalSite support and ask them to enable showing status on the account.
Additionally, be sure to request that PMW implements the scheduling pop-over, so prospects remain on your site and don't bounce away to ShowMojo pages.
Once enabled, this will automatically add schedule-a-showing buttons to your listing pages.