Noll,
I was in the same position as you a few months ago.
For the Befreiungskriege, the only dedicated Prussian caisson is from Magister Militum in the UK:
link
MM Have really international services, but since you're in my old home county, that's not really an issue.
Personally I like the slightly more sturdy equipment from Old Glory 10mm.
Now Prussians used either own and British Equipment.
What I did was get the Russian caisson sets, the wagons look like the Perry Prussian ammunition wagon posted by Artilleryman above.
You can then either (a) get an extra set of Prussian Limbers to get you the right outriders, (b) Use the Russian outriders as they are, (c) use the Russian Outriders and file down the Shakoes to Prussian style. 10mm is really forgiving about this kind of thing.
British caissons come with outriders in Tarlton helmets that don't work for Prussians.
Personally I went for Russian caissons with Prussian outriders.
Hope this helps mate!
Elliott