Is your spar by Z-spar? If so, I have ordered parts directly from them. You might be able to get what you need new.
Also, the folks here at SBO have helped me find parts several times. Give them a call and see if they can find replacements.
Last, if you don't care if it is an exact match but just want something that works, check out Craigs List. I have found booms, masts etc. on CL many times... actually I found a mast for a friend just yesterday on the Minneapolis CL.