You can normally get the front fork spacers from your LBS, but the rear ones are harder to find since many bikes come in a box with the rear wheel in place.
I got a rear one from St. John Street cycles but it wasn't any use. It was supposed to fit 130mm and 135mm OLN, but it only really worked in 130mm.
You can knock one up yourself using a piece of threaded rod and some winged bolts and washers (available from your local DIY store).
Will