Be Prepared...

As Ernest mentioned, just call around to a few brokers. Prepare to be shocked, though, because to be properly covered you'll probably want it to be 'business-class' insurance, seeing as you're servicing these machines 'as a business for financial gain'. The rates are liable to be MUCH higher than residential. However, if you go residential and then make a claim, and they find out you're doing it for profit, they may just deny the entire claim and leave you SOL...