they do exist.

i’d just pick one up on bestbuy’s site (their store brand, on clearance, $20). i’ve had good luck with their brand for other video converters (have ones that go usb to vga, hdmi to dvi, and dp to hdmi).

they’re also easily found on azn (for even less. look for ones with both a good rating and many reviewers). get one to try, then get a second one once you’ve checked it out.

note that these are all probably not bi-directional, and that converters that go the other way (composite to hdmi) also exist–so be careful when buying that you get one that goes in the correct ‘direction’ you need.