Are any private charters from USA to Sri Lanka?

That wouldn't be a charter; that'd be a transport (which tend to be no frills). You might check into going aboard for the annual migration although I think most cross the pond on transport ships these days. Charters generally leave and return to the same port. Probably a better idea would be book charters in different areas and/or book onto cruise ship transports.

If you pay enough, you can certainly charter a yacht, or ship, to anywhere in the world.
I will be happy to help: We have a small charter operation in Florida right now, but I just may purchase a big boat, hire a crew and book your charter to Sri Lanka shorty thereafter with your $5 million deposit down, and the other $5 million paid at the day of departure.
Happy to help, really.

I thought Sri Lanka was supposed to open up air travel again at the end of July ...is that not happening?

Under 10 days from the USA to Sri Lanka? 9,000 miles so you need to travel 900 miles per day, should be
37-40 miles per day for a plain great circle route, but there may be continents or islands in the way, and minor things like ocean currents and bad weather.
You need a very fast yacht with a huge fuel tank and double crew to pull it off.
Again, it is doable but expensive, see www.odincharters.com if still interested.

I would buy 2 $10,000 first class tickets, and pay an RN to sit next to you and administer enough sedatives to make you not care, followed by enough stimulants to wake up and walk off the airplane. Use the $25,000 you save to have a nice time while there.

I'd charter a plane and spend the full $50k plus. Where did you come up with this idea of chartering a yacht one way only?

That's actually a real possibility, and about the only one.
"You're afraid of flying a few hours and want to spend weeks bouncing around on a boat? I'd get over my fear of flying REAL QUICK"
Don't forget a few days of sea sickness puking your gut up.

He would have to pay to position the aircraft to the US or back to the US.
Plan a minimum of 6 figures ++

Sea travel would likely be more than 10 days from anywhere in the U.S. except Hawaii, maybe, if that's a major issue. Many ships make multiple ports-of-call.
Freighter travel is difficult to arrange, but maybe possible. The agencies that book that sort of travel represent very few of the cargo lines that operate. To arrange travel aboard a freighter, it would require contacting different shipping lines direct. You could possibly begin by contacting freight forwarders in West Coast ports and ask which lines run the route. Somebody imports all the cotton goods that come from there. Also, line up a source for expedited Covid testing so you can jump when they say jump. I've been on the lookout for freighter travel opportunities for many years, and discovered that getting from A to your desired B is not easy. An enjoyable way to travel, if you like your own company or bring some with you. There's not many frills, and sometimes no one speaking English as their first language aboard. I did have the opportunity to try to learn some Ukrainian, once, though

I'd have to think that today between Covid, terrorism and hijackings it's pretty hard to find freighters willing to take paying passengers. At least on anything you'd trust. Maybe he should buy a snail boat, point it west and sell it when (if) he makes it to his destination.

Me too!

Not sure where on that site you're looking, but I believe you're looking at charters IN Thailand, not going to, and on small boats. These are charters like several here do where they'll take people out for a few days island hopping. You can rent a boat here for about $50, but I hope you don't try to cross the ocean on an 18' Silly Lilly skiff. Seriously, fly commercial or charter a jet. If you want to take a trans-Pacific or trans-Atlantic cruise get rich and buy a yacht or hire on as crew.

It's not saying anything about chartering to Thailand, It's chartering in Thailand. Starting and ending in Thailand.

Well don't know if Covid have changed the picture, but CMA CGM out of France used to offer just this.
https://en.wikipedia.org/wiki/CMA_CGM

Shipping company, page with ad video
https://www.cmacgm-group.com/en/group/voyages-en-cargo

Booking page.
https://voyagesencargo.com/

This route stops in Colombo.
https://voyagesencargo.com/lines/columbus-jax-singapore-usa-indonesia