I'm not 100% sure, but it sounds like you're describing something like the press-fit arrangement that Best uses in their IC cores? This isn't the best angle, but you can see the caps in the top of the core in this image:
Those cores have a brass wafer that's pressed into the top of each chamber to retain the spring. (Rekeying those locks involves driving a punch tool up from the bottom of the lock: it pops the caps off and pushes the pins up through the top, but often destroys the spring in the process.) I'm not sure if they're the same diameter (likely?), but you could always check out your local locksmith and see if you could get a few from them: I'm sure they have bags of them, and would be happy to give you some for a dollar or two.
The other possibility, if you have access to a tap-and-die set, is to do something like what Medeco does with the screw caps on their mortise cylinders:
Depending on what cylinder you're starting with, though, there may not be enough metal in the "bible", or height in the chambers to make that particular solution work well. (Plus you'd be changing the construction of the lock slightly, which probably isn't your goal.)
Hope that gives you some ideas, anyhow!
