I purchased the Accuquilt system for this purpose. Cutting strips of most widths is a breeze anymore and takes only minutes to cut yards and yards of fabrics just the way I want it done. I am not sure that it would cut those dimensions but for most cutting needs it is great!
Other than this I would use the cutting lines on my cutting mat to make the cuts this way they should be accurate to each other. I also believe Cricket is making a 12"x 24" ruler now that could be of great help. It is available at JAF. I also believe someone else is making one now but I can't recall who?? This would be another choice of a way to go.