I am level 36, but have barely touched the main quest. So far, I have killed 5 or 6 dragons total. I hear others complaining that there are too many dragons. Maybe they start populating more after you reach a certain point in the main quest? If so, that would explain my lack of them so far. I really don't mind it, other than I need to absorb their spirits so I can do more shouts!

You already give the awnser to your own question.

More come when you get further into the main quest.

As far as I know, the only quest you need to do is Dragon Rising. It's the quest the Jarl of Whiterun sends you on with Irileth to kill the dragon at the Western Watchtower. Completing that quest should open up random dragon attacks. I don't believe there is any need to go further in the MQ.

the further you are into the MQ the more dragons appear..there's a quest you do about midway that adds a lot more possible dragon spawns, won't spoil it though..

I don't think the dragons that are "in the ground" in those inverted dome shaped bocci ball courts come out until a certain point in the MQ.

However, the game goes through dragons spurts. I only saw one dragon last week, real time. However, this weekend, I was tripping over them each time I started a game session. I even had 3 dragons in 3 fast travels in one session on Sunday.

I`m glad Dragons come and go randomly. I saw one Dragon that flew over me several times. I was out in the open and dashed for cover. Now bear in mine I am using the Deadly Dragons Hard Mod, and I wasn`t ready for a fight. It circled me a few times and then just flew away. what a relief!

But even without this Mod, I like th way Dragons are not automatons that will attack you every single time.

Oh yea, and the more you do the quest the more they come, so I do the quest very... slowly...

correct sir, that's the quest i was talking about, the one where that stuck up blonde girl takes you to that dragon mound and alduin is there, then he raises that dragon, after that, the dragons in the ground start coming up and you can see them

LOL, Bocci Ball! I used to watch my grandfather play that. 40 years later, and I still don't get that frickin game.

Fast travel more, you will see more random dragons.

You need to progress the MQ - mainly these 3 (quest names only - no walkthrough info):
Then do a lot of Fast Traveling and you'll have plenty.