I generally recommend the following steps to put together a list of all cards in all variations of a specific Pokémon:
- Go to the Bulbapedia [Name of Pokémon] (TCG) article to get a list of all cards of a Pokémon
- Go to the article of each card to see if there are additional promo or deck releases
- Look at the article of the respective expansions / decks / products to figure out which languages they were available in (and if first edition / unlimited and reverses exist)
- On the card articles now aditionally go to tools and use “what links here” to see the Korean/Thai/Indonesian/T-Chinese/S-Chinese exclusive sets and decks the card might be in (their articles are the ones with (ATCG), (KTCG) etc. at the end)
- For recent Simplified Chinese sets which Bulbapedia might have not covered yet, use the setlists on the Pokipair website instead.
- For EX era serial code variants check against this spreadsheet for international and this spreadsheet for Japanese / Korean cards.
- Do further research for example on Pokumon
- For cameos have a look here and then repeat the other steps for those cards as well.
This topic has some additional information as well, like marketplaces to buy from. Welcome to Efour by the way, would love to see your collection progress here!