You can find Nobunaga dressed in such an attire everywhere: in videogames, figures, touristic pamphlets and even is statues dedicated to him.
While searching for references for such things, though, I realized that there's NOTHING about them.
As I could find Nanban gusoku belonging to Kenshin or Ieyasu, the only thing left concerning Nobunaga are mere "replicas" based on armors belonging to someone else on the assumption that Nobunaga wore "something like this".
An example of such interpretations can be seen in this armor exhibited at the Nobunaga no Kan at Azuchi:
The peascod breastplate of Japanese manifacture is decorated with a cross and Sanscrit characters of Buddhist inspiration on the chest.
It's a wonderful specimen, but despite the location, this armor doesn't belong to Nobunaga.
The description "admits" that the "Barbarian" items are there to give "an idea of Nobunaga's tastes", but they aren't his personal belongings.
This one probably is, but it's not a Nanban gusoku in a strict sense:
This kind of armors is classified as Hatomune gusoku: since Portuguese cuirasses were extremely expensive, Japanese artisans started to copy the style but used local materials and adapted the design to Japanese tastes.
At this point in history this kind of armors were more effective: the itamono (iron scales) was in fact the only material that could save against firearms, and the "pigeon-breast" design helped to deflect the bullets.
But even if locally manufactured, this kind of armors were still expensive, so only powerful daimyos could afford them.
It's important to note that compared to the "classic" yoroi, these were quite heavier: the average weight of a cuirass was around 6 kgs, but it's safe to assume that moving around with one was simpler, expecially because the fuctional resizing of the sode (shoulder plates).
Another interesting contribution to the issue was given by a recent exhibition at Centrair Airport in Nagoya.
A special exhibition called "Samurai Lab" was held there to celebrate the culture of samurai, and this armor was displayed:
Unfortunately, it's just a replica made up by one of those companies that sell props for movies or documentaries.
Once again, it's based on what was "cutting-edge" back then.
Of the same exact kind is this:
--And again, it's another "made-up" specimen.
The manifacturer explains in its description that the artisan took inspiration from Tokugawa's Nanban gusoku preserved at Kishu Toshogu... That, and a good deal of videogames, I guess!
During my depressing research, though, I did find something interesting at the Kawagoe History Museum:
You can see a pictorial evidence on a byōbu depicting the Battle of Nagashino.
Talking of folding screens and Nagashino I decided to try another route: I searched for portraits of any kind depicting Nobunaga in Western clothes of any sort.
And guess what? I found nothing.
Even on this portrait that I saw at Gifu castle, despite being surrounded by all kind of Western stuff, he's still wearing Japanese clothes:
The evidences are indeed there: it's reported on the Shinchokoki that in 1568 Shogun Yoshiaki presented him a cuirasse... So he owned at least one for sure.
But did he wear it in battle? Was he used to it? And if he did, how is it that nothing about it exists anymore..?