Not the easiest thing to get done... to make a mould for a one off vac form mould would work out very pricey. A lot of vac forming is done using a PVC materials as it is easier to form but then you run into heat issues with the material when it's in a hot engine bay and in turn it could deform. Most of these cam covers are made of heat resistant polycarbonate materials.
A lot of vac forming here is done for the retail industry for display purposes, which is the business I work in... so the moulded items aren't intended to be resilient to heat. I can ring a guy to ask if he can supply and vac form heat resistant polycarbonate, but it would be best to try and get a group buy going so as to bring the costs down on the set up and mould costs.
I'll get back to you on it soon,
Jamie.