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.
ebay, i just bought one
Rimfire Technologies and DIP are two separate companies. The trigger guard is available at DIP, it's not longer available through Rimfire Technologies. The machine work from DIP is excellent. It's not (never was) an assembly though, it's a stripped aluminum trigger guard. http://www.diproductsinc.com/Default.aspx Go here to buy a new production metal Trigger Guard Assembly https://www.rimfiretechnologies.com/ProductDetails.asp?ProductCode=15001 Old Answer, You should be able to use the stainless steel assembly from the Model 60SS. However, replacing the trigger assembly will probably cost as much as the gun is worth.
I have a marlin model 60 with a gold trigger..the price difference is not by much if any at all..they both cost the same. some gun shops will charge more, but most usually don't and charge the same. A model 60 with etching and wood work can sell for more than one with just a gold trigger.
The "New Model" 60 has a bolt hold-open lever that extends through the trigger guard. The bolt, bolt hold-open parts, trigger guard, and stock are different.
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
You can find the assembly manual for the Glenfield Model 60 by checking the manufacturer's website or contacting Marlin Firearms, as Glenfield is a brand associated with them. Additionally, online forums, gun enthusiast websites, and platforms like eBay or Amazon may have listings for the manual. Alternatively, you can also find digital copies of the manual on sites that specialize in firearm manuals.
Try ebay. I just bought a new stock for $60.I believe they had a couple trigger guards. Steve.
gunpartscorp website.
According to wikapedia it is a model 60 made for big 5 sporting goods stores. It has a gold plated trigger and stainless bolt.
This would be best left to a qualified gunsmith to perform.
None of my references say anything about a plating on these, but it replaced the model 60 which had a chrome plated bolt, bolt handle, and trigger.
Can not be answered without the name of the maker and the serial number.