Hi Ryan_,
Check out this person called Pippowicz on thingiverse
https://www.thingiverse.com/thing:2792487
He has got a fantastic 3d printed design for using new components on the C128's shift lock.
It so happens that they work quite well on the VIC 20 style PCB as well as the C64 mitsumi (I think that's the correct spelling)
style PCB keyboards.
The VIC 20 and some C64 keyboards had a round style and some later model breadbin C64's had a square style.
However, what I observed is that all the keyboard PCBs have the same square hole that the locking mechanism pressure fits into..
They seem to work fine for me in either case. The great thing about this gentleman's design is that there is no damage whatsoever to the original keyboards.
So in the event you can get yourself the original shift locking mechanism it can be very easily reverted.
The only drawback I found is that the new shift locking components don't have the a full travel distance like the original shift locking mechanism.
I got these switches at reasonable price.
AU $1.46 | 10PCS NEW 8 * 8 latching switch Button switch double row self-locking 6 feet
https://a.aliexpress.com/_d85pscj
That's not a problem with the design so much as the actual new shift locking component that goes into Pippowicz's design.
If you can find a locking switch with a better travel distance.......
I hope this helps some.....