As mentioned (and pictured) in the two links Walking S provided, there are a few sources out there.
H&R do limbers with 75mm guns in their French WW2 line.
H&R do limbers with 105mm howitzers in their WW2 German line.
GHQ do limbers with 75mm guns in their Polish WW2 line. (French gun, French limber, but in the Polish line. In the French line the 75mm gun gets a halftrack tow.)
GHQ do limbers with the 105mm howitzer in their WW2 German line.
So effectively you have the same kit from both vendors, except for the minor difference in uniforms (mostly helmets) between Poles and French. GHQ will look better (in my view), but H&R will cost less, and may be quite acceptable to you. Your call.
Another approach, which I have taken specifically for my Soviets, is to build WW2 Soviet horse-limbers by a bit of kit-bashing. The GHQ Soviet 45mm AT guns (and 76.2mm Infantry Guns) come with a Stalinets tracktor and caisson as tow. That caisson is actually pretty well matched to the standard Red Army horse limber for 45mm guns. All you need is to add two (or four if you prefer) draft horses, which can be found through any of the models listed above, or from PFC C-in-C with their wagon set. Any time you take a wagon that comes with four horses, and build it up with only two, you get another set of horses for your Red Army AT limbers!
Just some ideas. Your mileage may vary.
-Mark
(aka: Mk 1)
