Star Bulbs are a rare substance in No Man's Sky obtained via Farming Star Bramble plants at your Home Base or from the same plant in the wilds of Paradise, Tropical and Generally Pleasant Planets.
It's primary use is in the construction of Poly Fibre which is used in many high level Blueprints.
Where To Obtain
Here is a planet where Star Bramble grows that only requires the first 2 Portal Glyphs to dial:
It is a very pleasant planet that really stretches it's Paradise label with being somewhat picturesque yet not all that well covered in Flora and Fauna.
This planet also plays host to Gravitino Balls.