You need GE44 or #47 bulbs... these are the standard bayonet type.

The perspex can be bought from any sheet supplier... look in you yellow pages under SIGNS.. will have a few local suppliers of acrylic sheet.... standard size is 1220 X 2440mm though, so unless you want a lot, then find a sign guy that will cut you some down.
Youll need 2mm thickness to exactly replace, but i often use 3mm