How about the Ontario navy seals issue mark 3? its got a nice waterproof sheath and the carry is very versatile, it can even be strapped to your leg, and the attachment loop is removable,made in usa
you can buy it from an Ontario authorized dealer here
http://www.knivesplus.com/QN-497-Ontario.HT
you could also try the mission mpk10-ti
its made of premium grade titanium so is fully resistant to water, versatile in carry, supposed to have some sort of quick release system, made in usa
http://missionknive.com/index.php?main_page=product_info&cPath=1&products_id=4
or the bark river sandstorm, the steel they use is tested to be very waterproof in even saltwater and the knife is available in kydex.
other than those your best bet is to find a good knife you like that fits in a kydex sheath with holes and try to screw it on the molle sheath system
good luck
you can buy it from an Ontario authorized dealer here
http://www.knivesplus.com/QN-497-Ontario.HT
you could also try the mission mpk10-ti
its made of premium grade titanium so is fully resistant to water, versatile in carry, supposed to have some sort of quick release system, made in usa
http://missionknive.com/index.php?main_page=product_info&cPath=1&products_id=4
or the bark river sandstorm, the steel they use is tested to be very waterproof in even saltwater and the knife is available in kydex.
other than those your best bet is to find a good knife you like that fits in a kydex sheath with holes and try to screw it on the molle sheath system
good luck