So basically I'm playing as a Vanguard and I unlocked Marksman for the pistols and shotguns along with Unity and some other skills. I didn't quick-slot them at first and now, after unlocking another power, I can't find them in the bottom part of my HUD, where my powers are. I can only find the ones I quick-tabbed already. What do I need to do to see these other powers?
If you have too many unlocked, including some of the achievements, the power selection/wheel runs out of room. This is a bug, but one that won't be fixed if it still exists this long after the game's release.
There are a limited number of powers on the Power Wheel. ... Your bonus Talent may disappear when you unlock all your abilities. You can work around this by mapping the talent before the power disappears, or by selecting a weapon talent.
(Source: Mass Effect Wikia - Combat-Related Bugs)
If you have weapon specific powers, such as Marksman for the pistol and Carnage for the shotgun, and you have too many powers to display at once on the HUD, then it will show the power specific to the weapon you have equipped at the time.