Hi mate
Im a conveyor belt splicer and use uncured rubber most days of the week.If you go to any of the splicing companies and offer up a carton someone help you out with some offcuts.I would myself but in WA.When you heat up the rubber it has to have pressure on it otherwise it bubbles up like an aero bar.For example we do repairs to belts with a small vulcaniser and it needs 60PSI
Hope this might help.
Sean