Is it OTC?
Yes, a quick google search showed Amazon and Walgreens selling it online.
You can get betadine liquid from horse supply stores. I don’t know what you would have to do to it to make it a nasal spray.
I thought that it was for topical use.
Bottled Betadine is a skin disinfectant and it is typically on drug store shelves among first aid supplies. Nasal irrigation bottles, distilled water and packets of powder to make up saline are also on the shelf (e.g. NeilMed Sinus Rinse kits), typically among cold/flu treatments.
Saline nasal irrigation can be soothing and help clear gunk. Some doctors recommend adding Betadine to the solution for anti-viral activity. You'd need to do a little research on appropriate concentrations if you decide to try this. Excess iodine can be irritating and shouldn't be swallowed. It's also important that any water used to make up nasal irrigation fluid be sterile. You don't want to squirt tap water up your sinuses unless you especially enjoy sinus infections.
Betadine is OTC. Related products are Budesonide and Xlear, but they use different formulas. NAC is another product the feds have been attacking, but it is not a nasal spray.
You can’t get it in America now. I bought some from Canada quite a while ago.
I’m using Budesonide, OTC, in many flavors.
The most recent study by Oxford University (randomized control trial) showed a 90% reduction in hospitalization for people with COVID.
Povidone iodine is readily available on Amazon and at most drug stores. Just mix a capful with water in a Neti pot and rinse. It stings a little, but no worse than accidentally using iodized salt instead of regular salt for the same.