TLDR: This is a list (incomplete) of companies that advertise with Reddit and put money in its pockets, and some contact forms for popular companies.

Brilliant Earth (www.brilliantearth.com - scroll to bottom and choose contact method)

Universal Studios (https://www.universalstudios.com/contact/general-and-miscellaneous)

Microsoft

Focus Features

Mitsubishi Motors (https://www.mitsubishicars.com/contact-us)

IBM

Intuit

Autodesk

Electronic Arts

Ally Financial

Discover

Up Australia/Up Banking

ClearScore

Noosa Yoghurt (https://noosayoghurt.com/contact/)

BMW Mini Cooper

Adobe (https://www.facebook.com/Adobe/)

Adidas (https://www.facebook.com/adidas/)

Adrenaline Australia

GameStop (care@gamestop.com)

H&M (https://www.facebook.com/hm OR https://www.instagram.com/hm/)

Liquid I.V.

Oatly (https://www.oatly.com/contact OR https://www.facebook.com/Oatly/ OR https://www.instagram.com/oatly/)

JOE & THE JUICE (https://www.joejuice.com/contact)

Excedrin (https://www.excedrin.com/contact-us/)

Rayovac (https://www.rayovac.com/contact-us/)

Nespresso (https://www.facebook.com/nespresso/ OR https://www.instagram.com/nespresso/)

Novo Nordisk

BackMarket

Caliber Fitness (support@caliberstrong.com OR https://caliberstrong.com/contact-us/)

Lucozade (https://www.lucozade.com/support/)

Moen

Uber

HP

Tezos

Truebill

Ulta Beauty (https://www.ulta.com/guestservices/contact-us)

MeUndies (https://meundies.kustomer.help/contact/how-can-we-help-HyfOyZn0o)

Lagunitas

Aviva

Beyond Meat (https://www.beyondmeat.com/en-US/contact/)

Bitstamp (support@bitstamp.net)

Hootsuite

Zoetus

Wolt (https://explore.wolt.com/contact)

Fineco Bank

Alienware

Tails.com (https://shop.tails.com/contact-us/)

Duracell (https://www.duracell.com/en-us/contact/)

Creative Assembly/Total War: Warhammer III (https://www.totalwar.com/support/)

Finder Australia

Virgin Galactic

Bungie

Discover Financial Services

Capcom

Allergan Aesthetics Coolsculpting