Crawling / Identifying Sub-Domains

I am looking for a one time service from a freelancer, who could help us to identify all existing subdomains from a url. I don't know if this is possible at all, but I hope to find the experts here ;-).

So, if we would chose a domain, e.g. abc.com, we would like to identify all existing subdomains, like orange.abc.com, apple.abc.com, etc

Is this possible an could you offer us a solution?