I understand what you're trying to do. I have a pile of PH sights but have never found any of the inserts.

However, if your goal is simply to shoot using the PH sight, GEHMANN makes a whole pile of lenses with variable apertures for target shooting. You can buy them with PH threads, too! Most combinations are less than $200 USD.

Here is one example:

https://www.champchoice.com/mc-optic...olor-filte-570

I have a 530-PH that fits all of my vintage Parker-Hale sights, has magnification as well as adjustable iris:

https://www.champchoice.com/mc-optic...nification-530

If you really really want all the 48 color filters, you'll have to spend twice as much on the 546-MC

https://www.champchoice.com/mc-optic...th-polar-546mc