Contractor insurance
Hasherucf,
You should be able to get coverage from anyone providing "hangar-keepers liability" coverage (usually the same companies offering aircraft hull insurance), however costs vary substantially and some insurers are more flexible than others so you will have to ring around. When I did this 6 years ago I was able to get a good deal by limiting my coverage to aircraft less than 5700kg, less than 10 seats etc. so make sure you explain the nature of your contract well.