iPad & iPhone - What country was my device originally sold?

I live in the UK and I bought a pre-owned iPhone last year from a London-based company, and when the Sleep button needed replacing (free by Apple even outside of warranty), staff at the Apple store said that because the iPhone was originally sold in Japan they wouldn't cover the free replacement. Well, I nearly fell off my chair when it was suggested that I ship it to Japan...

Even out of their short warranty period, the London-based company said they would go halves on replacing the button (I've been quoted £50). They are a good company to deal with, so...

I just purchased a pre-owned iPad from the same company and I have asked them to let me know where the device was originally sold because I don't wish to have problems in the future. They have yet to respond because I don't think they have access to such information other than going to an Apple store and asking staff for a polite favour.

So, my question is, does anyone know how to check where a device was originally purchased without putting details into a third party website or making a trip to the Apple store that may end up fruitless?

Many thanks.