I can't find flyer templates in letter size, all seem to be A4, Why?

Wondering if this is even the right group on support, as it’s a “general” question. I am trying to find / download templates to modify for a project for a job. I am in the USA and every template I find for Indesign / Flyer is A4. Nothing that remotely matches or any flyer I find searching is Letter size, all are A4. Is there a way to sort Letter vs. A4 for templates? Sorry that I expected more Letter sizes, I know Envato is not USA only, I did live and work in the UK for a while, but now I need Letter size. Thanks for any tips.