While there are sometimes sources for risers, they often aren't inexpensive, there is another way to make them yourself some.
The trick I used on my ST1100 was to get an extra set of bar clamps and simply turn them upside down, put the bar on and then the top clamps. Works like a charm on most bikes. The amount of rise you get varies but lots of times it is enough. All you need are longer bolts but they too are easy to get.
Its easy to check if this will work, just take the bolts out of the top clamps and raise the bar enough to put the top clamps underneath upside down. If they fit, all you need is an extra set.
One benefit you get is a space between the upside down clamp and the bottom one through which you can route wires if you have that need. Its an easy way to keep things tidy, just sheath them so they don't run on any sharp edges.
