I'm looking for suggestions for a tritium front sight I can put on a Model 10-5 that will work without milling the rear sight slot. In other words, it fits in the sight picture offered by the rear slot. Do not want to pay for re-bluing of the frame!!

I know XS sight systems big dot is too big, but have no experience with their standard dot.

Check out Tooltech. I remember them installing Trijicon tubes in existing revolver fixed-sights. I don't know if they still do that, though.

You might also be able to have a gunsmith remove the existing front sight and mill a dovetail to install a front sight with a tritium insert with dimensions similar to the factory front sight. I'm not sure how much that would set you back or if you want to do that much work to your gun.

I think this is your best option.