Since the front and rear sights should be equal total heights above the bore C/L, a little measuring should solve your problem.
Measure the height of the rear sight's sighting notch above the bore CL with the sight in the middle of it's elevation range thus :
Measure the notch's height above the top barrel flat, then add 1/2 the thickness (measured across the flats) - that will give you the total rear sight height.
The top of the new FO front sight from the bore C/L should equal that measurement/calculation.
See which of the available sights comes closest to that measurement when mounted - the rear sight's adjustment range should be able to accommodate zeroing for small differences.
Failing that here are several different FO front sight makers online, where you should be able to obtain the front sight height and color (more on that below) you need.
FO sight beads are available in yellow, green, red, amber & God knows how many other colors - all to accommodate the color perception of the various buyer's eyes.