First welcome to the forum and to the Cub Family
Your C-3 although made by Danco for IH, is supported still by CaseIH. See your dealer for the parts you need. Check the manual server at the link below and read the Owner's Manual for your C-3 Mower, it may offer some insights for you.
As for the removal process, well I must defer to those more experienced pro's who will definitely pop in and help out, but in the interim this should help a little. Spray a lot of Kroil, PB Blaster, Loctite Solvo-Rust or your favourite penetrating oil. This will help in the removal process.
Oh, if you know part numbers or one of the guys on the forum can give them to you, you can check out availablilty here: Case Tractor Parts On-Line
Hope this helps a little. And again, welcome