I guess the best place to enquire would be a the Fiat parts dept on Monday morning. Good to go with the van reg or chassis number.
There is also a Fiat forum somewhere on the web, so there maybe someone on there who could help. I would imagine a mounting bolt would need to be high tensile which probably won't be available at a motor factors or B & Q over the weekend anyway.
I doubt anyone on here would know which bolt you were talking about, let alone the size of the bolt or the pitch of the thread.
Spruce