i think now the only way to find parts is to buy a used gun from someone to fix your own.
I would go to Gun parts Corp. and find your JC Higgins model and exploaded view of your firearm.Then find the part number you need.they will tell you if they have it in stock.If not you may get the info you need to find them out in the general public.
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.
Google.
Try gun shops, gun shows, egunparts, garage sales, estate sales, etc..
Try e-gunparts.com
Gander mountain usually has them.
theres a website j.c. Higgins model 88 has the exploded view with parts list
You can find it on the Crosman web page. The JC Higgins model 180 was made by Crosman Air guns. See the link below
Try e-gunparts.com
Marlin Firearms
I have quite a few. sales@countrygunsmith.net
www.histandard.info