What you will need to do is go to the trailer and look for a model number or at least the MFG to get the correct arms for your awning. If the awning still operates, the sticker in on the left side of the tube when the awning is fully extended.
Electric or manual?
I would get the information required and Email this guy
for used arms or you might pay dearly for the new ones from the dealer. This ebay seller has used surplus for about $40.00 per set.
Speaking of the dealer..... Did you buy the unit new? You could just call the dealer and ask them for a quote on the new awning arms.
Also, look in your packet for the awning manual, it will have a parts diagram in it.
PS: MAKE SURE TO SEARCH IN THIS FORUM FOR AWNING REPLACEMENT... THE SPRINGS IN THE AWNING TUBE WILL HURT YOU IF THE PROPER PROCEDURE IS NOT FOLLOWED during replacement.