I can't get any tech companies in my building. If I try to get one, it says I can't have a tech company because I don't have enough tech companies.

How do I get my first tech company?

It is just my guess, but haven't you started with the medium- or large-sized office, by any chance?

I believe that the smallest offices do not have this restriction, and you may build a few of them to unlock the larger ones.

(I know that you have asked this question 3 years ago, but this forum seems sooo empty... And maybe someone else would have the same problem? :) )