Starting an AR15 build...

[hsiddall]

Ive seen and purchased a lower parts kit, but is there such thing as an upper parts kit (IE gas tube Etc...). or does some of it come with the barrell. I already have the quad rail system.

 

[Onmilo]

Most of the manufacturers that offer barrels, offer packages that include everything that goes with or on the barrel assembly.
That includes the gas tube and pin, the flashider, front sight/gasblock, a delta ring assembly etc.
You will usually get a set of A2 handguards but who cares, at the realized savings over buying everything seperately you can go ahead and pitch the handguards or sell them cheap at the next gunshow if you don't need them. HTH