If you have all the pieces, and know any welders, you 'might' be able to get the parts welded back together. It'd be fiddly and a bit of tweaking may be involved to get the stuff into line correctly. Worse things have been done in the name of practicality.
You are pretty much going to have to do some digging around and find out who made it for Sears, and what model or sub-model it is. This will open up the possibilities of finding the parts you need from the used gun parts guys.
They typically go to the gun shows and bring much of their stock with them, I have yet to find one with any sort of store front operation. Another good reason to go to a gun show once in a while!
Western Gun Parts in Edmonton has about the only sorta storefront operation I know of (there, contradicted myself, but, whatever) and are worth a phone call. They are supposedly better about dealing with emails these days, but I would phone them first. They may be able to sort you out right away, or they may want pictures (hint: Pictures really help! Including pictures of the broken part if you have it) sent so that they can ID it and match the part from their bins. They only work weekdays.
Best of luck!
Let us know how things work out.
Cheers
Trev
