I recently tried to replace my end caps through Fiamma and found the process incredibly frustrating - their web site appears to be designed to confuse rather than help. I finally stumbled on Panther RV supplies out of Washington. They had the parts and were very easy to deal with. I don't know if they have them in black, but white was readily available. I mistakenly ordered the end cap for a different awning than the one I own, and they took back the wrong prt and supplied the correct part very quickly.
I have ordered Fiamma parts from Panther as well. We somehow broke the center strut attachment and they had the part that no one else seemed to have, including Fiamma.