Hi!
I recently visited Paris and went to all of the above mention places.'
The Guimet museum had a couple of blade, a dozen tsuba and an armour on display.
The Musée de l’Armée (Les invalides) had ca 8 armours and a couple of blades of different periodes.
I also went to the shop espace4 - They where very helpful and gladly let me inspect their nihonto and fittings. They sat me down in a sofa and brought out nice blades after the other.
Top service and customer friendly.
There is also a litle antique shop at the Louvre antique center with a litle of everything Japanese related. there was blades, fittings, armours, bow and arrows , matchlocks etc.
Tip! I you like Japanese culture there is a book store in the reception erea on the Japanese culture center near the eiffel tower. They had all sorts of books on Japanese cooking, art, history, martial arts, nihonto, architecture, language and fiction. most of the books is in french, but many in english as well. I bought several nihonto related books there.
sincerely
Trygve