Hello Bojan,
You could start with brass machinery shim as it is easy to cut with scissors/knife or punch and bend as required and available in 0.05mm to 0.25mm thicknesses, sometimes as as a kit or thinner & thicker individually.
Some ebay possibilities:
http://www.ebay.com.au/sch/i.html?_o...+shim&_sacat=0
You could even, if you wanted a specific, non-available size, cut the spacers/washers from a feeler gauge set, although this is often stainless steel, with some brass leaves.
What led you to be concerned with the sensor tilt- any image differences in corners? In addition to any optical comparisons, it may also be possible to also measure this mechanically using a dial indicator and finding the distance between the camera mount flange and sensor (being careful with delicate glass, of course). BTW- check that the mount flange is OK and no sign of movement/deflection. There are some excellent inside camera shots on some camera disassembly websites that may be of use to see what sort of adjustments or shims, etc... would be possible. Most sensors have a 3 point to camera chassis mounting, sometimes with thin washers. You could also carefully "machine" these washers to thickness, as required if they are between the body and sensor.
Best
JA