hello... those Fans have a motherboard connector and are intended to plug into the SYSfan headers... and an adaptor would be a waste of $$$.
if you search for 120mm there will be plenty of choices with a standard 4-pin molex that you want... direct connection will result in full speed operation only.
most Motherboards are capable of multi-speed operation/control... but require a 4 wire/pin PWM connector similar to what your SYSfan header is.
does my motherboard have ports for the fans?http://us.ncix.com/products/?sku=78392&vpn=B75M&manufacture=ASRock
my case also has a 120mm fan