Finding replacement reflectors for these would be tough, as they have not been in production for about 30 years. Even if you could salvage them from another one they'd likely be in poor condition. The plastic reflectors in these things had a nasty habit of cracking due to the heat induced by the bulbs, and then catching fire as the hot bulb fell of place against the plastic. Many municipalities replaced these units en masse due to this problem (and also so they would not have to stock the expensive colored bulbs.)
So, I'd recommend you fabricating new reflectors out of aluminum if you could.
Visit Sir Marbelot's site for more info on these signals:
http://home.att.net/~njsignals/