A "real" tractor dealer will have a boneyard out back. It will have all kinds of stuff he took in trade over the past 20 years. I bought a good condition working JD sickle mower from a dealer boneyard for $600 New ones cost $3000+ and are all hydraulic. This was an old fashioned one from the 50' or 60's that still works fine.
A new "city slicker" type dealer probably has a new lot inside the city limits and wasn't in business 10 years ago at that location. Suburban land is expensive and he won't have a bunch of junk out back in the weeds. Look for old time dealers from all brands. You may find your perfect JD item out behind a New Holland dealer or vice versa. Once an attachment is old, no one cares about the original brand. That is what spray paint is for. Once I get time, my ugly yellow Kingcutter rotary mower will be converted to JD green.