I read that old Western Electric tubes are very collectable in Japan and bring a high price.. If so, must they have a certification that they work? Is there an outlet to sell them.
There is no such thing as certification or that they must have it. A buyer in a market such as Japan who is willing to pay top dollar for a WE tube is going to want a detailed explanation on how the tube tested and on what equipment and that the equipment has or is currently calibrated.
Most importantly a prospective buyer is going to want to know that the seller has a good history of selling tubes and primarily focuses on selling tubes.
As for an outlet it looks like you already seems to know to that based on your recent post so let's use that for another example. Are you prepared to back up your product with a money back guarantee if the item "isn't as described"? the reason is that a buyer can decide any number of things contact the site and ask for their money back and 9 out of 10 times they will win and the seller is stuck paying for return shipping and refund in full.
Speaking of shipping, shipping overseas is not for the uninitiated, you'll will have to package the item so protectively so that it arrives unscathed, on top of that you'll have to fill out customs forms, insure the item for its full worth, pay a hefty amount for the shipping & insurance and above all else hope the item doesn't arrive damaged or broken.
A lot of folks stumble upon a rarish item and think "Wow I just scored, this/these sell for lots of money" but if you don't have bona fides selling said rarish item buyers are less likely to take you seriously let alone pay you top dollar.
If I understand your username correctly you like to fish? I know next to nothing about fishing but I do know that certain vintage Orvis fly rods go for a ton of money. Let's say you were in the market for one and willing to pay top dollar would you wanna purchase it from a seller (me) who doesn't know much if anything about it other then what I've read online? or from a seller who has a history selling fishing gear specifically rods?
Again all of of this is predicated on your initial post and not seeming to know much about the current product you have other then some cursory internet searchs.
If I'm wrong I apologize