I have a Hunter ceiling fan (about 5 years old). The remote that came with the fan has gone missing, (I suspect a certain 3 year old). The fan is located where I cannot see the part number.

Is there any type of universal unit from Hunter or others that will work without having to replace the receiver as well?

Best to just buy a universal replacement with both receiver and remote. You will need to get up high enough to open the canopy so maybe its worth the effort to do that now and get the model number. You can't just go out and buy a universal remote by itself and expect it to match the right frequency.