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there have been some posts here on home-made versions of this, using hex-heads or some other. Perhaps a search will reveal them. If I recall the thread spec on those bolts is odd enough that it isn't stocked in local hardware stores. 4mm is it? I don't know the specialty stores here as well, maybe the store you mention would carry those...
I have a 12" Bintel (GSO) and just ordered the BOb's Knobs for all the collimation bolts. I don't think they sell one for the center bolt, and in fact you don't want one for there. The bolt head of the center bolt on the secondary is designed to fit just so into the hub of the spider, allowing the bolt to "pivot" (wiggle) while still connected to the secondary. This permits the variable positioning of the secondary by the three coll bolts. It's the compression spring over the bolt, between the secondary and spider hub, that "locks" the secondary mirror in place while adjusting the collimation bolts. Dynamic tension between the spring and the bolt(s). If you swapped out that head, you'd lose that anchoring-but-still-wiggly feature of the secondary center bolt. Plus, that center bolt should never really need adjusting once the secondary is centered under the focuser, so it doesn't routinely get adjusted as do the coll bolts....
But, yes, I share your trepidation regarding dangling a screwdriver over one's primary mirror. Such a thing...it's just not...natural. I always lay my tube horizontal on bed while doing it, thereby practically making it impossible for a screwdriver to damage the mirror. Short of a sudden change in the direction of gravity, or a poorly timed earthquake, of course..
Regards
Scott
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