Try e-gunparts.com, Shotgun News, Gun List, local gun shops, gun shows, etc..
Syracuse Arms Company ended in 1908.
Syracuse Arms Company was created in 1888.
50-100 USD or so
As far as the steel parts Gunparts.com can help ya but im still searching for new wood.
Blue Book of Gun Values
the internet
Gun Broker, Auction Arms, American Arms
No. Very dangerous.
On the but
No public records
Triplet Steel was a mark used by Syracuse Arms and Western Arms Corp was a trade name used by Ithaca about 1928-1945. I can't remember all the history right now, but somewhere Syracuse became a part of Ithaca, so I'd say your shotgun was probably made around 1928-30. It's purpose was most likely for hunting but possibly for trap shooting.
Try your local gunsmith. The Riverside is a Stevens shotgun. If you can find out which model it is, you can probably find the wood at Numrich Gunparts