XTZ is EU. As is Arendal. Shady just did a review of one of the Arendal Subs, in fact, and it was pretty impressive:
We were pleasantly surprised at our first encounter with an Arendal Sound product when they sent us the 1723 Monitors earlier this year, and maybe “pleasantly surprised” is a bit of an understatement; “blown away” is more apt. It wasn’t the least expensive speaker out there but we found it to be...
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BK Elec is UK.
American companies, but possibly available to you: SVS and Monolith by Monoprice.
(Rythmik, Hsu and Outlaw are likely not good candidates for shipping overseas.)
In Canada, Nathan Funk (Funk Audio) and Harbottle are known to make very good Subwoofers. Nathan's work is burgeoning on the bespoke level. Dunno if he ship overseas.
Considering your main Speakers are open baffle, you may well need to look for something highly specialized. Sadly, Transmission Line Subs are not very common these days outside of DIY. Something like that, though, with the right driver would likely couple with your room better and be easier blend with you mains. Of course, a product like that is not small.
We have one member here that designs all of his own Speakers and is a huge proponent of TL designs.
@TLS Guy might be able to help you out if you wanted to pursue something custom, perhaps.