Do a Google search for each of your main keywords/phrases + forum. (Using an asterisk means you want to search for all forms of that word - dog, dogs, etc.)
For example:
dog* + forum
pet* + forum
animal* + forum
veterinarian + forum
. . . etc.
Bookmark the good ones, because you'll be coming back regularly to check in on the conversations there.
In each of the niche forums you monitor, watch for the: