Brownell's Force 44 is popular with gun smiths- according to Brownell's.
I would use a low temp silver solder - with good flux - tin the sight thinnly and the spot on the barrel, thinnly. Would work better if the sight was hard silver soldered onto a base, like the turtle sight has, before low temp soldering it to the barrel.
That is how I would do it, the first time. Barring that, I would hard silver solder a sight that I filed out of a block of brass, to the barrel, like the turtle (for strength), but with a wider blade that I could see.
If not wanting to use a base and just a blade, you would need to cut a groove for the sight to sit in, for more 'purchase' area for bonding strength. For that, hard silver should be used, imho.
Hard, meaning high temp some call silver brazing.