As Stikpusher notes, the Italeri kit is available. I've read of a 1/48th scale vac-u-form kit, but it's pretty expensive. The Italeri kit is not bad, but it has a few problems that need correcting.
1. The cockpit is nothing like the real thing. Expect some scratchbuilding there.
2. The struts and wires for the rear tail section are missing. Scratchbuild.
3. The window in the top fuselage... Try as I might, I have been unable to find an image of a WACO glider with windows at Normandy. Some claim to be, but the absence of "Invasion Stripes" (especially on the top of the wings) leads me to think they're either from later in Market Garden or Varsity. I checked with the National WWII Glider Pilots Association and they replied:
One of many minor changes made during the approximate 3 years of CG-4A production. Can not give you specific dates as I have never seen a Field Technical Order for installing those windows, TOP and BOTTOM. It may be that this type of change was not suggested as a field change but only occurred as a production change order for the contractors. At any rate based on photos, 42 contract gliders do not seem t have the top windows, but 43 and 45 do. It is difficult to know if the top and bottom were added at same time but by 1944 it seems that the 43 contract serials and the 45 contract serials that started production in August 1944 had top and bottom windows. The window was actually four smaller rectangular shapes in a quad. They were mounted in the fabric same as were the round side windows. The rectangular windows did not abut down the center line front to back. They were separated several inches apart -- pairs of two side by side with a space between.. Google images and you can find top down photos to give proper location of top windows. Ignore the pics of models as they seem to have the incorrect size and are too far forward. There is a pic of the Gibson glider in the NMUSAF in which can be seen the bottom windows.
Charles Day
On my own build, I chose to fill the window in and smooth it over since it was not accurate to begin with.
There's a couple of other minor details, but overall it's the best WACO CG-4A model available, and Italeri also makes a 1/72nd scale C-47 to go with it for towing.
If you want a Horsa, you've got a LOT of available models! Lucky Brits!
Gary