Pokémon Center exclusive Elite Trainer Boxes are only sold at pokemoncenter.com — they're not available at retail. Because of constrained supply, they typically trade at a 20-40% premium over the standard ETB equivalent on the secondary market.
In Mintlytics, PC-exclusive ETBs have a red PC Exclusive badge in the catalog. Their product detail page links to pokemoncenter.com and notes the exclusivity premium so you can factor it into your hold/sell decision.
Modern era examples: Prismatic Evolutions PC ETB, Surging Sparks PC ETB, every SV-era PC ETB. Older sets (Crown Zenith, Silver Tempest, Lost Origin) have PC variants too.