This longtail keyword generator will help you to create boatloads of keyword ideas from just a few.
Use lists of seed keywords and common additions or endings and you will have dozens of keywords in no time.
Want an example? Here is one off the top of my head:
dog brushes for corgis
dog brushes for labradors
dog brushes for huskies
dog brushes for dalmatians
dog brushes for german shepherds
You could then add further variations to the second (blankets for, treats for) and third (more dog breeds) columns.