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

Most sign writers/plastic suppliers will usually sell offcut pieces, usually large enough to make several plastics from, without them having to cut a large sheet (which will cost more). I always use polycarbonate plastic sheet to make pf plastics, as i always thought perspex would be too brittle. I DID find that to be the case when i started trying to make my own plastics, using perspex, i've had them break while trying to drill them for the post screws  Polycarbonate seems to be more durable.