Here is link for mercury parts express It's getting some maintainance done but you might be able to find a parts list thru google.

http://www.mercurypartsexpress.com/us/

Once you have the list or part numbers go to a Ebay

Here is an aftermarket power pack for $115

http://cgi.ebay.com/ebaymotors/_Boat-Parts-Accessories-Gear__MERCURY-MARINER-SWITCH-BOX-POWER-PACK-OUTBOARD-3-6-CYL_W0QQitemZ150268236697QQadnZBoatQ20PartsQ2cQ20A ccessoriesQ20Q26Q20GearQQadiZ2823QQcmdZViewItem?ha sh=item150268236697&_trksid=p3756.m14.l1318