here's an easy way to find them (you need Crowbar or GCFscape, which open VPKs)
you can use your own version of TF2 and look for the in-game files for the default coordinates

tf > tf_misc_dir.vpk > root > scripts
in this scripts folder you will find the tf_weapon_scattergun (and all other weapons') files
These are the same ones we use to get VTF crosshairs, smaller explosions, etc except they're in .ctx form instead of .txt (basically the same thing)
These will contain all of the game's default values so you can figure out the coordinates from there

Just keep in mind the sniper crosshair has to be moved 1 pixel down to be centered. Also the sapper + engineer build/destroy crosshairs are actually just the corner of the medigun cross, not an actual crosshair

*edit* fixed, if anyone else is having similar issues try setting "crosshair" to 1 in console

bumping this, having some trouble with the installation- followed the instructions verbatim, and I don't have a no explosions script that could be causing any issues. are there any potential conflicts with mastercomfig and its .vpk's? tested it on the default hud as well in case there were any interferences with the hud crosshair I was using, no luck. any help would be appreciated

bump; is there a way to make the centre dot green?

here's a tutorial
https://www.youtube.com/watch?v=HbRH1AhSlzo