Banpresto released many postcards starting in 1998, and there is also a thread dedicated to these postcards on e4 (even though the thread was discontinued …)
However, I recently got hold of postcard No. 166 which was released in 1999. It features an incredible artwork showcasing various Pokémon atttacking. It’s amazing to see this unique composition of Pokémon and the vivid colors. In my eyes, this is truly a stunning postcard. 
Best,
orannge