Howdy,  I'm just now thinking about adding optics to my AR, and I was thinking about something small and preferably inexpensive, to screw into the carry handle.  I've seen a few small tubes perched on rifles here and there, but I've no idea what make or model.  I'm looking for light magnification, non-illuminated, and if it's an old german-style 3-bar reticle that much the better (though I don't think that's realistic).  Anyone have ideas for me?

Well if you must, look for the Colt branded 3x scopes.  They show up now and again here at EE, it has a heavy duplex reticle for short range work, there are newer models that have lit reticles too.  
I got one years ago and then graduated to ACOGs on flat tops.  Thought I'd keep it because it's a Colt, but there's no collection value in it so I sold it [brick]
Compared to the ACOG and newer scopes, the Colt/Realist is old technology.  I just looked through an Armalite 2.75x scope, also made by Realist, the sight picture is yellow, probably because it's so damn old (almost 30 years old)

If a more traditional designed scope will work for you try the bushnell elite 3200, Leupold vx I or II, burris fullfield, or lastly and certainly not least anything IOR makes.

its not "small" but i have a simmons Pro50 on top of my 22-250 and it collects ambient light like a champ!!  [url]http://store3.yimg.com/I/scopesforless_1733_3325871[/url]

Specialized reticles - contact Premier Reticle of Virginia.

Inexpensive scopes -  you can probably get a cheap scope for about $30 plus shipping plus a lot of praying that the scope will be acceptable.

Scope that you will have for years and not dump the next year - consider one of the compact variable scopes by a NAME manufacturer that will be in business next year.  Example, a Leupold 2x7 compact.  Or a Burris.  Understand that a scope with good coated optics like 4BAC and a low power will achieve two results:  light gathering in low light and present you with a wider field of view than a high fixed power scope.