those adapters are not recommended even if you find one. there is a reason the psu does not have the right connection, cause the manufacturer knows it can't power it.
easy enough to google "4 pin molex male to a 6 pin psu connector" if you insist on trying it. plenty of hits that way. you should get one that combines 2 molex into a single 6-pin though. at least that way it can pretend to provide enough power. a single molex won't even pretend to provide 75w for you.