you can go through new holland website but i tend to just go through place i bought my 555c from due to it is only one click and i am to the parts catalog.
Construction Equipment-Backhoes-Mini Excavators-Skid Steers-Pat Kelly-MO
once at above link. in middle of page click on """New! New Holland Online Parts Catalog"""
once the page loads up. type in 555c in search box. and then click on plus signs on engine parts. to find the cable you want.
myself i tend to just order from patkelly, since they gave me a descent deal and been quick in shipping orders to me. but i would think any local tractor dealer / tractor repair place near you can order the parts you need. regardless if they are ford/newholland/or other manufacture primary seller of certain types of tractors. other words ""open phone book"" look up "tractor repair" and if not that then "automotive repair"
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new holland is pretty good from what i have seen to list all parts and diagrams of parts.
as far as "shop manual" for the 555c i suggest that you buy it, it costs a 100 to 200 bucks but it is about 5 inches thick. and is very detailed info in how to uninstall and then diagnose and repair and reinstall everything in step by step notations in the book for everything and how to adjust and set things.
between the shop manual and the online parts catalog, there not a whole lot left. beside asking others were you might start diagnosing certain problems.
i take that back i prolly should get the operators manual. it has a few listings for type of oils to use, and how to run tractor and backhoe. but beyond that. pretty detailed info. and half the time i see local tractor dealers / repair places having there own dedicated "dealer login" to see pricing and info for parts. vs guest access to just see part numbers. that the above link gives.
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i don't have the shop manual in front of me. but when i had to adjust my throttle cables. some warnings, be carefull with the plastic cover that surrounds the right side dash. i had a couple wire bundles right in line with a good path to take the lever apart to hook cable up and re-adjust it. and had to take almost entire right side dash apart. if you need to lift the panel up with all the switchs on it. due so slowly and without much force. there be a lot of connectors in there. and only about half of the connectors are used. ((you have canada and US standard wiring built into your wiring harness (makes it a mess in there)))
you may want a second person to help you. pull foot peddle up or push it down. in order to get cable connected to hand lever. second person also helps when adjusting cables. ((trying to get in on left hand side of tractor while making adjustments can take the longest amount of time vs actually doing anything else))
all i have to say is make sure you have the wire clamps down and tight. it can be a rather pain and frightening experience. when going down a dirt lane. and not be able to slow down the engine due to one of the clamps came loose and won't allow you to slow down beyond shifting to lower gear and then into neutral.