Sorry to hear your rigging was stolen! What kind of person would steal a mast and boom!?!? I hope it wasn't another sailor. maybe somebody sold them to a scrap metal dealer??
Where do you live? That will deterine which option is the cheapest for you. masts and booms are very expensive to shipThere are spar manufacturers on both coasts, and they deliver goods by truck. You want to piggyback on their scheduled deliveries to keep costs down if you have to buy a new mast. But I'd guess finding a used replacement near you is going to be the cheapest alternative.
Get in touch with Rig-Rite. They specialize in replacement rigging for classic plastic boats. They know more than anybody about replacement spars for old production boats like the Venture. (except maybe the MacGregor Factory)http://www.rigrite.com/Spars/Rig-Rite_Spars/RigRite_Masts.html
Here's a list of spar manufacturers. Pick one nearest you. http://www.soverel33.com/Quicklinks/Spars/Links.html
1. Find a used mast in a boatyard near you. A rigger can help you select one that's appropriate.
2. find the spar manufacturer who is closest to you.
3. Check with the MacGregor factory to see if they can supply a drawing of the mast.
4. Do you have any new boat dealers near you? Can you adapt a mast from one of their boats? When they get a boat delivered to them, the factory can ship you an additional mast at little to no cost for freight.
Hope these suggestions help you focus your search and save you some time and money.
Hyde Sails of Northern California