Ok, getting into my first A2 build. Scored a RRA A2 stock and tube at a LGS for $20 today, but not spring.
I've never dabbled in rifles, always carbines. So please excuse the ignorance.
Looking online at springs:
http://www.midwayusa.com/product/585274/wolff-extra-power-buffer-spring-ar-15
or
http://www.aimsurplus.com/product.aspx?item=XSTSLA501S&name=Spike's+Tactical+Mil.-Spec+17-7+Buffer+Spring&search=buffer+spring

I'd prefer to keep my business with the smaller guys like Aim, but if the Spikes won't work (only buffer spring they have!) I may have to go with Midway or Brownells.
Any other recommendations would be appreciated.
I also wanted to know...will a standard spikes buffer from a carbine work in a rifle config? I can't see why not...other than weight?

Thanks in advance.

On a rifle buffer system, the buffer and spring are both longer than in a carbine system.  

If you use a rifle buffer or spring in a carbine tube then the bolt carrier will not be able to move all the way to the rear.  

If you use a carbine length buffer in a rifle length tube then the bolt carrier will not stop in time and the gas key will slam into the charging handle.  

If you use a carbine length spring in a rifle length tube then there won't be enough spring tension and the bolt will cycle too hard.

Rifle vs carbine buffer:

Thanks, that's pretty much how I understood it to be.
Like I mentioned, I've never owned a rifle before and never built one either. Always carbines. I'm hoping this is going to be a smooth shooter!
Any leads on a decent spring/buffer?

Doesn't really matter.  Rifle length systems are not all sensitive like carbine systems.

A basic rifle buffer should work fine, as will a basic inexpensive spring.  My midlength gas system works great with a rife stock/buffer/spring.  I'm going to try a spring from Damage Industries, only because they have a rep for lasting longer than a generic spring.

Thanks for the info!