My tips for finding pokemon merch:
1. Search on Ebay, avoid China or Hong Kong, it's likely that those two places are bootlegs (almost 100% of the time with China, HK is kind of a 50-50). Old, US merch is usually not made into bootlegs at this time.
2. Repeat the search every few days. Rare items may take a couple of weeks to emerge.
3. In the meantime, look out for social media sites with collection groups, such as livejournal.
4. If all else fails, commission one lol