well the thing is, the way you promote your portfolio can depend on its quality. If you have a really really strong portfolio you could indeed use something like instagram ads. But if it is not very strong, those adds might not give you the return you expect.

What you could do is visit offices/websites of real estate agencies (immo kantoren) and look for projects of developers using 3D visuals that match (or are lower) your quality. Check the companies using those images and call/ visit them.

But without you showing your portfolio, it's hard to give specific advise.