Ceiling cornice

Now, I know I said I wasn't going to be doing this again, but I'm set painting again, this time for 'Gaslight' at Old Mill. I was asked last night if I can do a suggestion of decorative cornicing at the top of the flats, but this is impossible to do with mere paint, so it's going to have to be real cornicing. Obviously the plaster type is going to be too heavy and expensive, but there is a moulded styrene foam type which would be the perfect alternative - only I don't know where to get it from. Can anyone point me in the right direction? Thanks, Tim Prosser.