Local gunsmiths, gun shows, e-gunparts.com, Mossberg... those are the places to try first.
If your rifle is still in production, contact Mossberg. If not, contact Vic Havlin at www.havlinsales.com. Mr. Havlin and his wife Cheryl run the Mossberg Collectors Assoc. Be advised that a bolt is not simply a "drop in" but will require fitting to the gun. Improper headspace is a very dangerous condition that can arise when a bolt is too short.
Mossberg customer service- Telephone: (800) 363-3555
Does not exist.
You may want to try Gunbroker.com / gunsamerica.com / gunparts.com / ebay.com / and the mossberg company if you have not done this yet and see if the can help.
I believe the Westernfield rifle was made by Mossberg, and is the Mossberg Mdl 353. Magazines are available from Havlin Sales. You can order through their website, or send them an email. Very nice people to deal with for anything Mossberg.
100-1000 usd
No.
that rifle is the same as the Savage/ cooey/ lakefield-mossberg 64. you can buy direct from Savage Arms.
Yes you can put a bipod on any rifle.
I'd try Numrich at e-gunparts.com first.
wal-mart
Gun stores, sporting goods stores.