For long tails by GEO specifically, Google autocomplete with the location set in the search settings does more than people expect. Type the seed and work through the alphabet, a to z after the term. Tedious but it shows what people in that country actually type.
Keyword Planner gives volumes but the ranges are wide unless you run ads. I use it to confirm a keyword exists, not to pick between two. People Also Ask boxes are the other free source worth mining, those questions are usually low competition and easy to answer properly.