Just out of curiousity, I did a
model search on the Deere online Parts Catalogue (
Link ). Just click on the Model link and enter "380".
It lists the 380 blade for the 655/755/855 and 955 tractors. It lists the 380A for the 670/770 tractors (770 is the immediate predecessor to the 790). It appears that the blade is the same, but the frame mounting components are different. So, if you just buy the blade (and hydraulic components!!!!), you should be able to get the mounting components from your Deere dealer.
Now, it might be costly...it'll depend upon your intended use. If it's for snow removal, a rear blade might be considerably cheaper and still let you use the loader (I assume you got the FEL?). If you've a long drive or large area to clear, a rear mount blower might be a better option.
There is also a blade that mounts to the 419 loader, but I think it's a manual adjust type. As mentioned, depends what you want to use it for.
BTW, I own a 790. I think you'll find it to be a nice machine for a smaller (5 to 8 acres or so) lot or farmette. Pretty tough machine, as was my 670 (which was traded for the 790).
Good luck!