Jack, New Holland uses a special type of 3/8" connector for the FEL connections. I've never found a substitute at places like Tractor Supply that carry hydraulic adapters and fittings. Last year I tried another adapter and it did not work. Luckily, all I had was bad o-rings making my QC adapters leak and was able to buy them from my NH dealer for a couple of $ instead of buying new connectors.
EDIT Here are your connector part numbers from Messicks.com
Coupler, Quick, 3/8" Male - 86583622 $20.19
Coupler, Quick, 3/8" Female - 86583553 $29.27
These fittings are shown in the attached diagram, Items 28 and 29.