Photos of a drop tank recently on-sale on the Japanese ebay. The owner knew nothing about it, so no information from that end, except that it's 203cm long and 50cm wide. The tags could have shed more light but they are in bad condition and we can barely read some parts of them.
The top kanji in the circle reads "A" (as in Asia), the other reads "mokusei" (wooden).
From the above tag we can only partially read the top inscription which says: "Gokoku No 4110 factory". "The term "gokoku" is associated with presentation aircraft in Manchuria, so perhaps this tank was manufactured there.
The other indication we can read is the "Weight: 19.6 kg".
Unfortunately we can read nothing on this tag.
After checking the drop tank designs of the IJNAF and IJAAF single engine fighters (Zero, "Raiden", "Shoki", "Hien" etc) it is safe for me to say that it's not a drop tank carried by one of them. Also, it's too long. My other thought is that it was probably used by a reconnaissance plane. It's too big for a "Babs" and too short for a "Myrt" (it's drop tank was 4 meters long) so my only other conclusion is that it could be a drop tank for a "Dinah".
If it's indeed an IJAAF drop tank, it offers a brilliant sample of the Army hairyokushoku standard paint.
By the way, it was sold for a mere 231,000Yen or 2,110$US.