I can’t reply to this directly but hopefully they see it!
For building master sets of Pokemon, I start with Bulbapedia and Serebii for general set lists and promos. Keep in mind they don’t often include reverse holos, so check to see if reverses exist for those as well. eBay and TCGPlayer are great for that.
I also look to see if anyone has created a list already. A lot of people have shared their lists on places like Reddit.
I also check eBay and I type the name of the pokemon and various keywords to find more obscure cards, keywords like “promo”, “championship”, “regional”, “signature”, and “error”.
Some errors are not printed errors, just one offs, which I don’t count. But cards like “no symbol” jungle cards should count and the error Dragonite from Team Rocket, for example.
Finally look out for base set variations. There are 4th print versions with a different year at the bottom of the card compared to the OGs.
Finally, getting out there in the community, online and off, and sharing your progress with others often sheds light on even more that we didn’t even know existed.
Have fun! 🤙
@DeepPocketMnstr
Hey pat 👋
I have a question about how you find pokemon for a master set of that pokemon 🤔 I ask because I want to start off my girlfriends complete master set of every single loudred in existence for her and give what I have in it for her birthday pls & thx.