I've picked up a BRNO ZKK 602 in .458 win that I've had reamed out to to .458Lott, but the front sight bead has been snapped off.

Who sells them?

Also, can a flip over night sight type bead be put in to that front sight base, which has the little button to hold the sight in place?

cz makes the same front sight, direct insert, for the 550 magnum. take the sight out, read the number on it. that is the height, in MM, and call cz, order that number, and the next 2 LESS for sighting in the lott.

or, you can order a racknegal/necg mill cutter, recut that base for necg inserts, and then you can use the HH "moonsight"