Try www.multitrip.com - the cost of insurance is based on the scope of travel (Europe, Worldwide etc.) and whether there is an underlying Health Insurance policy. There is no limit on the number of trips.
Not sure .. I know my employer has travel insurance which covers me when travelling on business for them and I suspect many other employers would too
However whether an individual could purchase such a policy I don't know ... But on the other hand I don't think my own travel insurance has any exclusion for business travel though (I'd have to read the small print)