I've tried getting the list of IP's under an ASN number for example AS8167 however I am having no such luck. I have seen that team cymru have an IP to ASN, however that is the opposite of what I actually need.
RADb has a whois server that provides this functionality. It includes information other than just the IP blocks, so you'll need to grep for those if that's all you're interested in:
$ whois -h whois.radb.net -- '-i origin AS8167' | grep -Eo "([0-9.]+){4}/[0-9]+" | head
189.11.64.0/18
189.31.0.0/16
189.72.128.0/18
189.73.192.0/18
189.74.0.0/18
189.74.64.0/18
189.64.0.0/11
189.0.0.0/11
187.52.192.0/18
187.52.0.0/17