In my country, there are many such chem websites, but most sell only to businesses. I have found one that sells it to anyone with disclaimer that their site should be used only by professionals. It's around 12 USD for 250g, but I am just too paranoid about them asking questions or authorities showing up. I thought about ordering other reagent and, if needed, lying that I'm a student writing about water treatment (SN can be used for that).
Also, there are tons of companies that sell "technical" SN in my country. It's still more than 99% pure, but comes in at least 25kg bags that cost about 70 usd. Also most sell to businesses, but I found one company that has few bags in stock on a marketplace similar to Amazon.
As someone close to chemistry (not a chemist tho, but was going to be one before some stuff happening) and done many experimets, the synthesis from the video is easily done, but I'm not sure about quality of SN, although it should be pure enough theoretically.