I've been trying to get these for some time, and finally snagged the opportunity. From what I saw of the dates on the bags, these are from the 1960s, but will vary. Please allow for dirt, preserving powder, wear, and possible corrosion on the metal parts (rust). These are all in great shape but were stored for many years.
Yes, you can pick your size! Make sure to check if your size is still available before ordering! You can do that by seeing the total "in stock" number right above the "add cart" button.
These are being sold as collectible items or for costume purposes, and not for any protection or wear against CBRN threats.
Regarding many peoples' concerns about asbestos in the filters: I don't know how to test for it, and don't know if these contain any. This research is up to you. This is why they're being sold as collectible items. Most of the filters I've seen so far have been dated in the 1990s, which was well after asbestos was known to be used, so again, take all of this in to consideration.
ITAR CONSIDERATION: These, for whatever reason, are restricted from export, and therefore this item CAN NOT be shipped outside the United States. Sorry about that, I would if I could.