Only the ones you're missing
Tick off the Pokémon you own in the free Pokédex Binder Tracker, then open its Print tab and choose “Missing cards only”. You get placeholders for just your gaps, in the same layout, and the tracker shows which binder page and pocket each one belongs in.
How to print them
In the print dialog choose Actual size (100%), not “Fit to page”, so each placeholder matches a real card. Each page holds nine, the same as one 9-pocket binder page; cut along the dashed lines. Thin card stock slides into pockets and sleeves more easily than plain paper.
How many pages for all 1,025?
All 1,025 placeholders print on 114 pages, nine to a page. In a binder they fill 114 pocket pages — 57 sheets used on both sides. A typical 360-card binder (20 sheets, 40 pages of nine) holds 360 cards, so a complete National Pokédex needs 3 of them. The tracker's Binder tab plans every page, including one binder per generation like the Japanese Pokédex binders.