Manual can be gotten in electronic form from sears at the searspartsdirect.com website (linked at end of post), where you can download manuals for lots of appliances, tools, etc. Flip up your tractor's seat and look for the model number sticker, should be near the battery if battery is under seat. You will need the model number (model, not serial) to find the right publications. When new, the tractor probably came with an owners manual and a parts manual.
Alternative: get your model number, google it and the term "parts manual," and you will probably get right to the info at several websites.
Amazon is a possible parts source, with some decent vendors and prices; I've ordered several repair parts for my 2009 YTS 3000, which is technically a model 917.289210. That should be the pattern for Craftsman model number: three digit number probably starting with nine, decimal point, six digit number. Note that my owners manual has a typo and omits last character of model number. Watch out for such printing errors; you might be actually looking at the correct publication but it's mismarked. Be sure to save a PDF copy of the manuals so you'll have them later. Craftsman Riding Mower Tractor Parts Repair Parts Sears PartsDirect
As for assembly, the parts views will be some help. Once you get the new part it might be pretty obvious. For example, there might only be one hole or hook relativley close by that other end of spring could attach to. In general, all the "parking brake" does is hold the foot brake pedal down in the applied postion, not much different from jamming pedal with a stick (no I do not recommend this method). Unfortunately, due to safety interlocks, you need the parking brake to work if you want to leave the seat while tractor is running, as you've probably discovered.