You are not required to buy the flag, but it is respectful to fly it. Fly it lower than yours. Screenshot the flag and find a company that can print flags.

The Islamic section is for nations with Islam majority or beliefs.

Members: 

The Soviet/Communist section is for Soviet/Communist nations.

Members: Kybia, NSSR

The Christian section is for nations with christian majority or beliefs.

Members: South Kapia

The Other section is for nations that don't fit in the above sections, or don't want to be in a group.

Members: North Kapia, New Wirges, Sunland