If you cant get a direct replacement quickly, you could:

1) Buy a 15V power supply or a universal. Universals are easily available and many have a 15V setting. Then clip off the connector from the old unit and graft it on to the new one.

2) Buy a 15V/universal and the appropriate one or two adapters that will get you to an F-type connector (example set of two RCA to F, 3.5mm to RCA )

Since the original had coax coming out of it, take steps to minimize the new cord acting like an antenna: keep it as short as possible, wrap it in foil, etc.

Adding to the TV/Channel 3 advice, be aware that not every modern TV will work.

They may technically receive NTSC-style channel 3 on paper, but some will have problems, but receiving analog television to the proper specs isn't exactly a top priority nowadays. I've seen at least a couple TVs struggle to display correctly.

Before, we had these huge switches to toggle between the console and the antenna, but nowadays you can just pick up one of these RCA to coax converters.

If you don't have any luck, it may be worth checking out one of these RF to HDMI converters. I haven't tried them myself, so I can't vouch for their quality, unfortunately.

Last resort, if you're skilled enough and able to do the work (or have a friend do it), maybe you can look into what conversion mods there are to support composite output.

Ignore those post downvotes -- feel free to drop back and let us know how it goes, or if you have more questions. 😎