At a dealer of the engine brand or possibly at a mower junkyard. If going for the latter, make sure it is not bent.
One can find reviews for the Atco lawnmower from the 'Lawnmower Review' website. They have reviews for numerous Atco models on the site. Reviews can also be found on the 'Which' website.
look at the manual
A shaking lawnmower is usually a bent / broken blade. Don't continue to run the engine, because you can bend the crankshaft. Check the blade first, and if the mower continues to shake even with a balanced blade, then the crank shaft may already be bent.
model #
A manual for the Craftsman lawnmower model 944.607853 can be ordered from the Craftsman company. Another option is to contact the store where the lawnmower was purchased and have them order a manual.
oil will run away from crankshaft and become dry on rod thus rod is is dry no oil rod breaks comes out side of block
A Murray riding lawnmower owners manual can be obtained from most Murray riding lawnmower dealerships. You can find the owners manual at most local libraries.
At a Briggs and stratton dealer.
http://www.planopower.com/store/honda/index_mowers.shtml
Briggs and Stratton Website THE INTERNET!!!
The crankshaft sensor is located on top of the transmission at the passenger side.
Online. See the link for help.