I've been on the lookout for something suitably springy, such as some Belleville washers.

We used to have truck body front mount springs lying around at work, which would of been ideal, but sods law dictates when you need something, you can't find it.

If I can't find something soon, I'll just have to buy a suitable spring. This is one of those projects that's been continually shoved down the todo list, but is now rapidly approaching the top of the list :-/