"Judging by the $76 that I paid for 6 "O" rings (I kid you not)," Oh man that sucks.
Generally O-Rings are pretty universal, try to match the material for the application. I think that generally Viton O-rings are the best for most applications.
Don't match the new O-ring to the old one. The old one will be compressed, and the cross section diameter of the old one won't match the correct new one. You may have to buy 3 of the correct diameter and then try to fit them until you find the one with the correct cross section.
If you have the parts diagram, the original manufacturer may actually list the SAE O-ring part number, instead of some in-house part number. If that is the case then you can purchase the correct o-ring with no trouble.
Springs are tougher, if you have the parts diagram, it may list the specs on the spring (I doubt it). If you have a source where you know you can trust the quality you may be able to purchase three or four and see what works. I would be hesitant to go this route, maybe $30 is worth the reduction in time and effort to find a part that may or may not work properly for the next 10 years.