This may be a long shot but try a specialty plumbing place in your area. Not like a Home Depot but one that caters more to Plumbers and Heating Cooling companies. They may have the fittings as well.
Are you having to adapt into the radiator connections as well? I know on mine it's a 5/16 fitting. If you're using a 3/8 then how are you changing it? Just curious
One more thing- I've dealt with plumbing before but what is the -8AN? Somebody have a link that describes these in comparison to the regular Metric or SAE sizes?