Neil, I would be very happy with 6061 - it machines well and takes a polish. (Off the top of my head I think the rod I used for the section was 6061.) But the thinnest I can find (without spending ridiculous numbers) is 6mm. This is 1000 grade stuff - almost pure ally and soft as putty. If you happen to find a source for 1.5mm plate in 6061 or above I would be very happy!
Woody, my photography woes are driving me to drink at the moment - but that's for another thread!