This is really a question for someone involved with the site(s) you want to order from. The vast majority have contact forms or otherwise a contact e-mail address. A site like Fasttech is based in China (essentially) but accepts USD and US credit/debit cards. Of course they also ship to the US, either from China or from a US warehouse. Other sites in other countries won't accept USD/US cards and won't ship overseas. There's no one answer.
If a site doesn't ship overseas and has something that you truly want and truly cannot get elsewhere, you MIGHT be able to use some sort of package forwarding service, but that's much more common with people in other countries ordering FROM the US, not to.
A completely separate issue is whether or not it's safe these days to use a debit card for an online purchase, especially one with an overseas site. Personally, I wouldn't do it; there are far more protections on a credit card... but that's just me and not everyone has access to a CC.
