Do they make a RF Modulator which accepts both composite and component video inputs and provides a coaxial output for connection to an older TV?
RF could only do Standard definition, as the radio frequencies were only designated for analog broadcasts.
You will have to ensure your component is at Standard definition.
You can use this to convert component to composite.
http://www.hdtvsupply.com/component-to-composite-adapter.html
which is an expensive thing. $ 90.
You can then use a composite to RF modulator, which is $10.
There may be component to RF , such as old VHS tape records and so on, video “receiver” or “Switch” boxes but these would cost much more
You might find an old VCR will work. Some (especially the “middle years” high end ones) had both types of inputs and could output channel 3/4. Get one for $5 at a thrift store. Be sure to check the back panel carefully.
In most large metropolitan areas, you can put a metal stick on your roof (an antenna), run a coaxial wire from that stick down to your TV with an HD tuner and watch HD TV for free.
Radio frequencies carry Digital TV (DTV) signals quite nicely, including HD ones.
That’s composite only. The OP wants composite and component.
I see now. Also in looking the reverse issue was explored at some length here before.
Are there TV RF modulators which output digital/HD on channel 3?