About glowing asteroids

[Vezbot]

During all my time played on KSP, I have been really interested in capturing a glowing asteroid. I know they are somewhat rare but on my old save I managed to find quite a few, (I also used the debug menu a ton of times in 2018 on my pc so that's maybe a reason I have not came across any now). On my newer ps4 save, which I started in 2019, I haven't came across any at all. I find this to be weird cause I can't count how many of those things I captured and brought to planetary orbits, is there any specific limitations to spawnrate, or a specific size for a glowing asteroid to appear in the game?  

P.S. I don't use the debug menu now on ps4 cause it gets rid of achievements, also it's more fun to give myself a challenge and sense of legitimacy.