I'll give some unconventional advice but will probably be forgiven for it. Go search Facebook for the group "DFW Retro Computing." The community is very strong there. Listed there is also a scheduled meetup on Jan 25, I believe. I bet if you put a "shout out" on there, someone could be more than willing to help you check it out at the meetup, if not sooner!
I'm in that group as well, being a former resident of the area. I usually attend the quarterly meetups as well, despite living in Virginia
I'll be completely transparent: you'll get a much better response there than here...
You've probably already thought of this, but: if you are somewhat hardware-savvy, you could buy a DIN video connector from a place like Fry's, and solder it up to an S-Video plug (also from a store like Fry's), since 8-bit guy has shown us that Commodore's Luma and Chroma connections *are* S-Video.
Only if you are comfortable with a bit of soldering and are familiar with pin-out diagrams, of course.
The other alternative is to find a video adapter box from an old Atari 2600, which (I think) is the same thing.
Not the same thing. The "adapter" box used by the Atari 2600 (and most computers in the 8-bit era) is just an antenna switch (and balancing transformer) to switch between the RF signal supplied by the C64 and whatever antenna the TV is hooked up to.
Of course, if you have any working television in the house, you can use a simple $2 adapter to connect the TV's antenna input to the C64's RF output. You just need something like this:
**Temporarily out of Stock** Estimated shipping date 2/14/2020 Great device designed by Sven Petersen. Composite out. Mono or Stereo out (If your 64 has been modded with). Audio In.. SVideo out! This device makes hooking up your 64 to a modern tv quick and simple. Documentation: The...
In fact, I'd suggest NOT getting a DIN cable - get this, instead. This gives you the most flexibility for hooking to modern TVs.