I don't know of any off-the-shelf blade assemblies that would work for you, but you might try asking whoever manufactured the rake. They might either have one or be willing to make one for you.
Otherwise, you will have to make something for yourself either in-house, or with a contract welder or machine shop.
Hmmm.... Just thought of something else. You could get a quick-attachment mounting on the loader arms and a blade or bucket for that. Set your rake up to be used on it too. More bucks tho...........
Good luck!