Try wiebetech.com. Great service and great products. Email weibetech and ask them about bus powered options. I think it’s always better to use a power cord while editing but see what they say or do a search here on the cow for bus powered firewire.
If you have been using your system drive to edit, now might be a good time to backup, erase, and reinstall. Keep your media on the firewire drive and your project files on your system drive.