How can I get five Mushroom spores when the whole planet has only two mushrooms?

Solution 1:

It is possible to increase the yield gained from harvest, with the Wetlands Wanderer skill, from Gathering specialty (source):

Wetlands Wanderer is a skill in the Gathering specialty. It requires Forest Forager Level 1 to unlock.

It increases yield gained from the following plant resources: Amanita Mushroom Spores, Amanita Mushrooms, Crimini Mushroom Spores, Crimini Mushrooms, Rice.

Then your problem seems to be a known one, as this player states on this steam community post:

I had the same issue. Think it's a known bug they really dont care about, you know, being more or less game breaking.

This user finally had to cheat the game with a command in order to get his spores.