After seeing this question and some of the discussion on it got me wondering if this pair of Vanishing Cabinets was common or rare...
We know that Draco had to repair the cabinets after he realized there was a connection.
The other’s in Borgin and Burkes, said Malfoy, and they make a kind of passage between them. […] I was the only one who realised what it meant – even Borgin didn’t know – I was the one who realised there could be a way into Hogwarts through the Cabinets if I fixed the broken one.' - Harry Potter and the Halfblood Prince, ch. 27 ‘The Lightning-Struck Tower’
Then from the films we have this scene Mr. Weasley's Information
You can see the appeal, should the Death Eaters come knocking, on would simply slip inside and disappear for an hour or two. Could transport you practically anywhere. Tricky contraptions though, very temperamental. - Harry Potter and the Half-Blood Prince (film)
Dumbledore lead Draco to believe this was a very clever idea, and one that even Dumbledore did not think of:
Dumbledore’s sigh was half a groan. He closed his eyes for a moment. ‘That was clever… there is a pair, I take it?
‘Very good,’ murmured Dumbledore. ‘So the Death Eaters were able to pass from Borgin and Burkes into the school to help you… a clever plan, a very clever plan… and, as you say, right under my nose…”
However, my recollection of the story line was that Dumbledore essentially allowed Draco to carry out his plan. Dumbledore knew Snape had made an Unbreakable Vow with Draco and encouraged Snape directly help Draco. In the tower scene Dumbledore is just stalling and trying to get in Draco's head so that Snape will have have to be the one to finish the job.
Regardless of whether Dumbledore knew the cabinets were a pair or not, do we know if Vanishing Cabinets were produced as pairs or as stand-alone items or was the identical pair we see unique?