Anything that can't be bought can be made. I would just hold myself back from trying to make it look pretty.
Welcome to TreeBuzz by the way. Tons of knowledge and info here in the form of members (when they have time to weigh in) and old threads/discussions of topics. If you use the search function and type in various wordings of the topic of interest you can come up with different results going back years/decades.
Most of the hydraulic should be able to be handled by a local hydraulic shop. Pins and bushings can be done by a machine shop. A good welding shop should be able to install bushing, etc and fix cracks/broken stuff. We have our own machine shop and make pins, etc for our grapple truck. It's really not hard to deal with.