Welcome aboard!
Bikes that were fun to ride usually were worn out completely, especially boy's bikes. You may not find a good 24" Spyder like yours, but that 24" frame is not unique to the Spyder model. You can easily get that same frame and build your Spyder to be a duplicate of the 24" one you had, or you could make a 26" version that looks just like it.
It's a Murray frame, they made hardly any changes to their cantilever frames over the years. They were used by many brands, Sears like yours, Western Flyer, Foremost (JC Penney) and others.
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There are thousands of those frames, mostly 26", but plenty of 24" frames or whole bikes. That would be your best bet for your bike. You'll collect tons of parts along the way too.