You really need a table saw. Use a fine tooth blade with no offset to the teeth. If you look down the edge of the teeth, they should all be perfectly in line. Some blades have the offset (kerf?) and will chip the acrylic. Set the blade height so that it just comes through the acrylic and feed it slowly though. If you don't have a table saw, you'll need a 7 1/4" paneling blade for your circular saw. You'll need to clamp the acrylic to a table and clamp a board or piece of angle iron on top as a saw guide. Saw it very gently and you should be OK. Most Lowes and Home Depot stores will cut acrylic to any size you want if you don't have the tools or don't want to try it.
Logan J