Ranged combat has to be studied - then advanced ranged combat for the longbow.   not sure on the exact path to take to get to them - but i've never had a problem -  going for equipment - weapons - etc in no particular order until the bows come up....  sorry for not being more help -  I think there is a flow chart of the progression of techs some where.

For a kingdom it's weapons - ranged combat - advanced ranged combat

For empires it's offence and then either weapons of slaying or piercing weapons, can't remember exactly which.

Looking through the xml files containing the techs, they all have their <AppearanceChance> set to 100, so they should all show up all of the time.  Obviously StarDock built in the ability to have them randomly not show up for a given game (by setting the number to something smaller), but it isn't actually happening in the game yet.

Ranged also appears to be a bit weak. I regularily seem to miss or do really piddly damage with archers.

RAT  

Something I've noticed about ranged units.  There maybe a hidden secondary range along with the maximum range.  I've noticed that I can't hit things for crap if targets are out near the maximum range but if the targets come closer, say 4-5 tiles from the range units, they actually start hitting properly.

I'm not going to give details but during the campaign I had a group of 8 archers absolutely murder a high armor value target when it was only about 4 tiles away.  Before that point they couldn't hit the thing even if it was a barn.  It also had a lot of HP and my archers were capable of reliably hitting it multiple times for quite a bit of damage once it got close.