I'm sure you'll get a number of recommendations.. Kowas is well known and has a huge area to hunt. There are plenty of others. Here is what I would suggest. Go over to africahunting.com and to accuratereloading.com. Join both and spend a little time just reading hunt reports for Namibia. You will see several reports for the good operators. You'll get to see some trophy pics and find out some about the PH's.
Bruce