They did make some Clonetrooper blasters and rifles for Episode III, but for Episode II they were only CG. There was no real gun they were based on.
The original CG model of the DC-15 rifle is based on the combination of a couple of the 12" action figure guns which they used for the original scale model of the Clonetrooper.
The DC-15A blaster rifle that the majority of the Clone Troopers carry in Attack of the Clones and Revenge of the Sith is based off parts from the German MG-34 General Purpose Machine Gun from World War 2, which was used as the basis weapon for the BlasTech DLT-19 Heavy Blaster Rifle in the Original Trilogy, and components from the BlasTech E-11 Blaster Rifle that were carried by the Imperial Stormtroopers from the original Star Wars trilogy.
The DC-15A blaster rifle that was seen and used in Attack of the Clones and Revenge of the Sith appears to be a hybrid of the parts from the E-11 blaster rifle and the DLT-19 heavy blaster rifle of the Original Trilogy as well as showing that the designs for both the E-11 and the DLT-19 originated from the DC-15A blaster rifle.
The DC-15B blaster carbine that the Republic Clone Troopers carried in Attack of the Clones and Revenge of the Sith appears to look like a "de-evolved" version of the BlasTech E-11 blaster rifle the Imperial Stormtroopers carried in the Original Star Wars trilogy with the DC-15B carbine having features like foresight protectors, a blaster power cell located on the side of the blaster's receiver, and a folding rifle stock. The features that were on the DC-15B would later become standard on the E-11.
In Revenge of the Sith, the DC-15B blaster carbine was used by many regular Clone Troopers on a larger scale. The compact look and handling of the DC-15B carbine was preferred by many Clone Troopers in Revenge of the Sith over the bulky DC-15A blaster rifle the Clone Troopers carried in Attack of the Clones.
The wider use of the DC-15B blaster carbine by the Clone Troopers in Revenge of the Sith also provides more hints to the Republic Clone Troopers' evolution into the Imperial Stormtroopers of the Original Trilogy.
I did mention it before in one of my articles for SW Insider. I write the regular article Techinical Readout:Set Piece every issue.
I don't have a photo handy.
To address the Wikipedia info:
The DC-15 is based on the toy DLT-19 blaster rifle that came with the Hasbro 12" Sandtrooper not a real MG34. The proportions are not accurate to a real gun. The front half of the DC-15 rifle is based on the 12" toy E-11 blaster that shot spring loaded red missiles. This E-11 came with several Imperial 12" figures. Again the proportions are not accurate to a real Sterling (this one is way oversized compared to the Sandtrooper rifle).
So you can make an accurate Clone trooper rifle with those two toys but it would only be a tiny scale replica (unless you're 1 foot tall).
ILM scanned this tiny scale gun and cleaned it up for Ep2. They made the pistol version by altering pieces of the rifle CG model. For Ep3 the prop dept built some real life props from the CG renderings, but I'm not sure if they were ever used since the clones are all CG.
For the clones, the "head shots" were an actor (I can't seem to remember his name at the moment) that they super imposed on a digital body. They didn't even make any clone helmets for the movie. Again, all digital
Here is the rifle from AOTC it has different reciver propostion than that of the carbine.
Here is the Carbine
During my research I found that the rifle in ROTS is built direct off the carbine. The rifle that the Clone shock trooper is holding is a combination of the rifle from AOTC and the carbine. Here is the comparison I did to figure out the size.
Here is another variation of the DC-15 that is seen being held by an AT-RT driver in the new Chronicles and Dressing the Galaxy book. It is a CGI composite of the standard ROTS clone rifle and the carbine. They just merged the two files together.