It was the first vendor that you posted for the kits in the UK:
They said they might could ship a few sets over
Also, the 3rd link you sent also had a very similar window, which made me think that they might be more readily available on your side of the pond:
The 'official' marine brass ones are cool, but expensive. I just thought since I saw two UK manufacturers using the same (or very similar) round windows maybe one could buy them directly without going through the tear manufacturer. A couple of the UK links you send seemed pretty nice and reasonable priced. I couldn't get the US link that you sent to come up and when I search Stateside, there isn't too much round, though there appears to be one supplier as posted earlier, so I'll check that out as an avenue as well. Anyway, I think that the round windows look pretty classy.