Here's a place that provides replacement masts, etc for Sunfish. They are in Rhode Island. I have delt with them personally, and always satisfactorily. I even had them fabricate a welded stainless steel anchor bow roller (my own design) 20 years ago. They were very flexible. NB
http://www.rigrite.com/spars/A_spec_...ish_spars.html
EDIT; The boom material (underlined in RED) shown is 6063-T6 aluminum.