As you may know, a linguolabial consonant is when the tongue is articulated against the lip. These sounds are fascinating to me, as they sound at once like alveolars and bidentals. And unlike Radical consonants or complicated glottalized semivoiced tense implosives, they are not at all hard to pronounce, despite their rarity in natural languages. So I want to know:

Why don't they show up in natural languages that often, and
Why don't they show up in conlangs?

I don't understand how these sounds are produced. Do you have any videos or audio files? I like rare sounds. And I try to add them to my conlang. But first I myself have to produce those sounds.

I was going through some old files yesterday and found that I'd used these in a conlang I created about eight years ago. It was the language of a serpentine race and I had concluded that their thin lips made it difficult or even possible to articulate bilabials, so they substituted linguolabials.

It's easy to produce linguolabials. You just stick the tip of your tongue on the bottom of your upper lip, except for the linguolabial trill, which you are probably familiar with as "blowing a raspberry". I mean really, it couldn't be any easier, and it's just as exotic as aspirated tense semivoiced lateral postuvular affricates.

Which are so common in natural languages.

Is Talib sarcastically referring to the "easy linguolabials", which are so common in natural languages", or is he reffering to aspirated tense semivoiced lateral postuvular affricates, and he is trying to tell me that those, are in fact, not exotic at all and occur regularly?

Linguolabials are very interesting consonants indeed. I have a conlang that possesses them in its inventory.

I mark them as <ń> and <ṕ> for [n̼] and [t̼], but I now realize this is an inconsistent orthography for mixing in symbols referring to bilabials and alveolar consonants. How would you write those?

Well, the IPA says to put the linguolabial marker on the alveolar symbols. However, I say, that for your languages orthography, it might be better to diacritic the bilabial consonants, because they are much more rarely modified than the alveolars. Though I personally would probably use seperate letters for linguolabials, such as Ȣȣ, Φφ, Ƣƣ, Λʌ for [n], [θ[, [t, and [l respectively.

Take a wild guess. How common are uvular affricates in any language?
Completely arbitrary, or based on something?

No one's going to take the trouble to put theire tongue so far out for a linguolabial and even if they do, others won't and they'll just retract it into dentals within a few generations because of the general discomfort of sticking your tongue out. It's easy to pronounce, but it's hard to keep moving the tongue so far, especially in fast conversation. I mean it's easy to do the glottal stuff with practice, even in fast conversation because it is just a certain tightening of the throat at the right time in the right manner that doesn't require so much mobility. Try alternating between the linguolabial and retroflex positions quickly and see what I mean. Either the retroflex turns into alveolar or the linguolabial turns into dental

As for the uvular fricatives, nobody's going to waste their breath. It's just generally uncomfortable and would probably merge into a french R or a q eventually after a few generations. Maybe for emphasis on a q, but other than that it probably wouldn't appear that often. But it depends of course. The Vietnamese "kh" still has a little bit of affricate [kx] (it is half [x]) because of the nature of Vietnamese syllables to be choppy and separated rather than flowing and connected like Spanish or Hindi, correct me if I'm wrong.

What I wonder is why bidentals are so uncommon. My conlang uses them, even dinstinguishing aspirate and voiceless.