Just wanted to chime in, I had about 5-6 of these sealed at one point, now down to just 1 or 2.
From my research, I think a common source of these were the two pack base set and jungle blister:
These were also a common source of 1999-2000 made in USA Base Set Packs. Never seen a booster box of 1999-2000 jungle but I would think some exist.