Please be so kind as to share information about vacancies as soon as they become available.

Please be so kind as to share information about any vacancies as soon as it is available. 'It' refers to 'information' since 'information' is both singular and plural. Or you could say: Please be so kind as to share information about any vacancies that become available. Does this help?

you could also say ' please could you inform me if there are any vacant spaces'