Try gun shops, gun shows, garage sales, want ads, e-gunparts.com
Your Hawthorne Warrior M820B is in fact a Mossberg model 340, of which there were various designs. A lot of the parts are available through e-gunparts.com. But, be careful, and ask a lot of question when ordering parts. A lot of the parts are not a direct fit. I have a Mossberg 340KA, and had to replace the barrel. I ended up with a barrel from a Hawthorne M820B. The sights on the Mossberg barrel were dovetail mounted, and the sights on the M820B barrel are mounted with screws. That's just an example. This will get you started in the right direction.
Colt
There are a few places you can find a Rear sights for a Savage Model 120. The most popular place to look would be online or a gun store.
Looks like Savage built them. Their model SB100B. Hawthorne model name was "Vulcan". Parts are available from Numrich Gun Parts. Good to see someone else owns one.
100-460
Best left to a gunsmith
Compare to a known dated model, Blue Book of Gun Values.
No sn data available.
50-125 USD or so
Mossberg made most of the Hawthorne bolt action shotguns. They were sold as a Montgomery Wards special.
I think it may have been made by Mossberg or someone that made guns for Mossberg.I was at a gun show looking for parts for my Mossberg 20GA. model 185K and found a Hawthorne 20GA. model M149 It is the same gun, the end of the stock does not have the flare at the end under the barrel but all the parts will change from one gun to the other.
The Hawthorne Warrior M825 .22 LR was sold by Montgomery Wards in 1957 and 1958. It is actually a Mossberg Model 140 rifle.