I want some small rubber over centre catches, same as bonnet catches, but smaller, but can't find any. Can anyone help?

where are they for austen? and for what purpose? do they definately need to be smaller than the bonnet catches?

[Edited on 12/3/11 by daniel mason]

they are for holding on a front valance/splitter, not enough space for full size bonnet catches. I'd like the rubber ones so they are slightly sacrificial as i expect a visit to the grass could result int the splitter being removed, but would like the bonnet left in 1 piece sort of