Trying to find number of neurologists in as many countries as possible - ISCO88 the best source?

ISCO 88 has a category for neurologists - 2221 0-52.40 Neurologist

Will this be reported in an extract reported from that source?

Are there any other routes I can go to get this information?

Yes, this is the correct ISCO88 code for neurologists.

However, for census microdata disseminated by IPUMS-International, a maximum of 3 digits of the ISCO88 code are available. Many national statistical offices provide occupation codes that correspond to only 2 digit ISCO codes and some for only 1 (https://international.ipums.org/international-action/variables/OCCISCO#codes_section).

Currently, 3 digits are available in samples for 32 countries.

Usually the protection of statistical confidentiality is the reason given for limiting the number of digits.