Parts != Parts

So, I have been trying to fix up a couple of Squier Super-Sonics. Basically, I want to replace some corroded parts and put them back to stock. One of them has a weird set of third-party string trees. One has some of the bridge saddle height adjustment screws that were corroded, turned upside down and re-cut to take a flat head driver. There are a bunch of rusted, stripped pickguard and tremolo cover screws. The tremolo cover on one is stained with rust. Some knobs are chewed up. One of them has a three-way toggle switch that looks like it was deliberately cut off. The pots on two of them are in very bad shape and may need more than a spray cleaner.

I determined that the bridge of these is really a Fender American Stratocaster bridge, or at least made to the same specs, so the replacement tremolo arms and saddles from Fender made for that line fits perfectly. But the other parts?

Chrome pickguard screws/tremolo cover screws: they are just slightly wider and shorter than Fender screws. Because the screws are just slightly different, the tremolo cover is just slightly different too (the screw holes and the bevel around them is different).

Knobs: the kobs on the Super-Sonic look almost identical to the knobs from a Fender Precision bass, but the Fender knobs don't fit quite right. They are shaped slightly differently; the Fender parts have a set-screw, while the Super-Sonic part is press-fit. I suspect that they are the same knobs as the Japanese Mustang reissues, but I don't know that for certain.

String trees: Stratocaster string trees don't fit. Apparently the Super-Sonic parts have specially-sized screws and plastic spacers.

Three-way-toggle: not only is the replacement part not the same as the Super-Sonic part, but the Strat part won't even fit in the routed cavity.

So, I am now the owner of a bunch of Fender replacement pickguard screws, two toggle switches, a tremolo cover, two replacement pots, and some Precision bass knobs which I can't use.

And I'm deeply annoyed.

This seemed like a simple project, a quick and easy replacement for some of the damaged parts in order to make the instrument look as close to mint and close to stock as possible.

Wikipedia claims that a toggle switch for a Les Paul can be used, but after looking at the routing, I think that part is unlikely to fit.

Several scattered sources claim that these were built with American Stratocaster parts, but that really seems to be only true of the bridge and tremolo and possibly the tuners, and doesn't extend to any of the other parts.

Does anyone know where I could even find parts for these instruments?

UPDATE: it seems likely that the differences in things like pickguard screws might be as simple as the fact that we still haven't gone metric. I've been waiting on that promised move to metric ever since I was in grade school!