Where find 1/2 inch (I believe) hose fitting?

KTOT

Where can I find a female hose fitting that screws onto the filter next to the water pump (or screws directly to the water pump--same fitting size/type) in a 2017 T@b Outback? I believe it's 1/2 inch, smaller than regular hose ends. I tried a pipe thread fitting but that has the wrong type of threads. A regular hose fitting is too large. A plumber of 40 years (he claims) told me such a thing doesn't exist, but it's the ending that's on the hose that goes into the filter/pump and is the ending on the hose I have for another RV's winterization kit. I don't want to buy another full winterization kit, and the cheaper winterization pumps and such I find have the larger hose fitting to fit onto the city water connection outside the RV. Where can I find the proper hose end that has barbs at the other end to fit into clear plastic tubing?