It’s a big problem.
I had 3 bikes that needed tires. (Classic tires in not so standard sizes)
They all turned into a problem finding.
What I came to find out is there are really like 3-4 tire distributors that have 5-10 different websites that they sell tires on. They even have the same people working at all the website.
All the website have different pricing and shipping rate but are ultimately the same company. When 1 is out, they all are out and so while it looks as if their are a lot of options to buy your tires they are all just a false front.