You won't be able to buy Simon's goggles anywhere. You'd have to make them by scratch. My suggestion is to make the goggles out of craft foam and clear yellow plastic sheets.
[~Future Cosplay Plans~]
Dipper Pines [Transcendence AU - "Alcor the Dreambender"] (Gravity Falls) - 80%
Unbeatable Squirrel Girl (MARVEL) - 35%