Hi Jay,
I did a lot of work with these systems when i work for Dynamic Suspensions in Thetford. These systems have a major design flaw and people drastically mis-understand how they work, or rather that they don't work.
The Belvilles are easily sourced, drop me an email and i'll give you all the suppliers details.
darren@gtstuning.co.uk but if you really want to develop the car then you need to move away from the system.
Drop me an email and i'll explain all, might be best in a telephone conversation.
A quick explaination though is that people believe that by preloading the bellvilles is stiffens the car up in roll which is wrong! Because you preload each side against one another you are not preloading the system, as one side counter acts the other and equals zero-preload therefore the spring rate of the washer stack remains the same and so does your anti-roll rate.
The Bellvilles can be stacked in various arrangements which effect their rate and their travel etc. back to back and face to face changes things dramatically, but, there are equations in the catalogues to show these effects. The other thing to know is that they are not very repeatable in terms of load and rate etc.
There are some other issues with monoshocks in general, but, the end result is almost everyone moved away from the system and back to twin dampers.
D.