Hi
www.airride.co.ukThey don't appear to do kits for these vans, probably because they use coil spring suspension rather than leaf springs.
Overseas you could buy coil spring boosters that were incorporated into the shock absorber, so looked a small version of the McPherson Strut used on most European and Japanese vehicle's front suspension.
In America the Cool Dudes had/have those hydraulic shockabsorbers that they use to 'bounce' their cars, so I can't see why a similar principle can't be used.
I would get in touch with them and ask the question.The problems with these boosters is that it can become easy to overload a van without realising it.
The other issue is brake balance to the rear. There is a brake balance valve that reduces the brake fluid pressure to the rear bakes when the van is empty to prevent the rear wheels locking up under braking. As the van is loaded and the suspension 'drops' this valve automatically adjusts allowing a greater brake fluid pressure to the rear the heavier the load.
This automatic adjustment isn't too much of a problem on motor homes (Fiat Ducato chassis as the most popular conversion) as this valve can be adjusted to cover the higher rear ride height under load. (The difference between an empty homehome and a loaded one isn't that much.) But this may become more of an issue with our type of load where we start off fully laden in the morning with a full tank of water and as we use water through the day our load becomes lighter.
In the early Berlingo days, I know of a couple of guys that replaced their 600 LX rear suspension with units from an 800 LX. Depending on the model of Dispatch/Scudo you have, this might be another consideration. (It won't change your payload specs as that is fixed at manufacture. If you got a certified garage to certify a proper upgrade to a higher payload (Suspension, brakes, tyres etc) then they will re-register your van as a higher spec van and can carry a higher load.) With Berlingo's it wasn't cost effective to do that conversion. It was cheaper to buy a new van.
Edit;
Firestone make a unit for later Dispatches I have just found.
http://www.marcleleisure.co.uk/store/firestone-assisted-suspension-citreon-dispatch-0709-p-2381.html