I bought the blade from Lowes that is sold in the same area as the acrylic. The trick is to score it several times, then putting the sheet on a hard surface (I use my work desk) Put the acrylic on a table, with the scored edge slightly away from the edge of your table. Then, hold one hand on the side that is on the table FIRMLY and then with the other hand, press down on the edge that is sticking off the edge of the table. Do this quickly as to snap the acrylic apart.
Mind you, the only time I tried this is with the 8 x 10 size. The larger sheets, I will ask the clerk at Lowe's to cut it for me.
I hope this helps!