You could probably refit the window into the arm by using some strips of fabric and a good glue like Barge Cement...
I'd cut the fabric into short strips and then glue it to the glass and then to the arm. depending upon the amount of friction caused by the weatherseal around the door and the glass you may have to use heavier pieces of fabric to get it to effectively wedge into place.
Might be a cheap short term fix at least until you can find the parts to replace the glass.
One other idea might be to simply clean up the arm as much as you can and then insert the window glass, then epoxy the sh___t out of the whole thing. Better to have it out of the car so you don't epoxy the motor and anything else that might be below the window...
Although looking at the pics there might not be enough metal there to hold...