Search for authors on Google Scholar by their field of study and country
You can search multiple keywords with something like this:

label:robotics + label:machine_learning


in the author search. Narrowing by country can be trickier. You can potentially narrow by the email address. For example, if their profile is verified with a UK email address it will end in .ac.uk. Thus you can search:

label:robotics + label:machine_learning + .ac.uk


and only get UK researchers. You'll probably get some false positives and negatives with this technique so it's not perfect but will help narrow the scope.

Here's a related question pertaining to narrowing country on Google Scholar:

Google Scholar: how to exclude some countries from the search?