Visit the Numrich Marlin/Glenfield page. Or the Marlin home page to download the PDF version of the Model 60 manual. These two rifles are very similar in design.
http://www.gunpartscorp.com/catalog/Models.aspx?catid=310
Marlin downloads.
http://www.marlinfirearms.com/customersupport/manuals.asp
Numrich Arms has a schematic of it.
Try e-gunparts.com and Marlin
Age is 1966 from the AB prefix. You can find diagrams at Gun Parts Corp. web site.
Check at Numrich Gun Parts. They have a online catalog with breakdown diagrams.
you can search for it on google.
Contact Marlin.
Look for a manual for a Marlin 60. e-gunpats.com may sell them. Updated Answer - You can also download a free manual on the Marlin web site for the model 60 - it is the same firearm. http://www.marlinfirearms.com/Firearms/SelfLoading/60.asp
I cannot find any reference to marlin ever making a model 226.
00034810
You might try Gun Parts Corp., or check the Ebay auctions from time to time.
Which model??
At a good gunsmith's shop. Maybe Numrich's Gun Parts (search gunpartscorp) For the complete trigger guard assembly, including trigger, safety, springs, pins etc., you can get it from Numrich, Midway USA, Brownells or direct from Marlin. If it's just the trigger or other individual trigger guard parts you need, you'll have to get those from Numrich for a different model Marlin.