Use of existing corporate names in a map

I’m currently working on a map with many office-buildings, which I want to label with the names of the companies.

I’ve just found, that most of the company names I made up actually do exist.
Am I still allowed to use them in my (non-commercial) project, or can I modify them?

For instance, I’d like to use “Dawn Corporation” or “Dawn.inc” as a reference to the HL2-spraytag, but they’re both taken.
Is there a way I can use them?

I won’t start asking for permissions, because I need about 20 different names, and it would probably end up in a huge chaos.

Any ideas?

You should just avoid using major brands.
And whatever we invent, might be used somewhere.

I’m not planning on using “major” brands, it’s just really hard to find real-sounding company names, which are not already taken.

I guess it’s still okay to use my made-up names, if i put in a disclaimer like

Since you aren’t selling anything it should be all good. You don’t need to put in a disclaimer.

But if you make a play on a famous name, so it’s incredibly obvious what you mean, it’s much funner. I’d rather see a punny joke name than a random 100% made up one (unless it’s a major part of the map’s story)

Like this :v:

Hey if you want I can make a logo for you.
Photoshop Skills ^^^