I am not, in fact, familiar with "real" calibration, except in as much as I know that I can't easily do it with what I have to hand (I suspect that I might be able to rig something up, but the price of doing so would probably rival the prices for the three important calibration devices on eBay), and if I DID rig something up, I'm not sure I could rely on the calibrations that resulted.
My father apparently sent his 2213 in for regular calibration through the late 80s. That calibration appears to have been annual, judging by the dates on the stickers. I'm not sure why he stopped, but his service business started to dry up about that time, so I can imagine several explanations. He never bothered to get the 475 calibrated after he got the 2213. Again, I'm not sure why, but the fact that he was using a 60 MHz scope as his "daily driver" suggests that the 475 was well in excess of his needs, so maybe strict calibration wasn't too important either?
I haven't tried any significant calibration of anything, only small stuff that (hopefully) doesn't throw off the rest of the scope (e.g. adjusting the invert balance on channel #2, and recalibrating the V/div balance). I haven't touched the sweep timing calibration, for example, because I know that would require equipment that I just don't have.
My impression (from this group and elsewhere) is that you can still get these things calibrated by professional shops around the country (the place I'm looking at is www.custom.cal.com which has locations in New Jersey, Florida, and Oregon), and that it's not absurdly expensive (but more expensive than the old scopes themselves). I'm not sure what, if any, the extra cost is for a traceable cert.
I'm pondering the same thing you are pondering, if only because it would be a possible way to defray the cost of acquiring these parts scopes. Also, I only need so many parts scopes, and I'm well beyond that number right now. I also need only so many working scopes, and I am probably beyond that number as well. I'm not sure what obligations you are under if you sell a scope as "working" or "restored". If I were going to charge the kind of prices I still see for "working" 475a on eBay, I would want to include at least a front cover, pouch, probes, and operators manual, and the scope would have to be in pristine cosmetic condition (but that's just me and my ridiculous scruples).
The number of working scopes I need is a complicated question: While the 475 and 475A are on the bench (as subjects) I need a scope that I can use to work on them, which should be a 100 MHz scope (the 2236). However, the 2236 is currently on the bench (as a subject) so I need a scope to work on that one as well (which is either my father's old 2213, or the 2215A). The 2213 could also be on the bench, but I've given up trying to diagnose its intermittent channel 1 flakiness, so the 2215 is the primary scope for the moment, and everybody else is either a patient or a donor.
-- Jeff Dutky