Mike, each maker has a particular style of metal front sight insert that are usually not interchangeable between brands. But the good new is, the threads at the back of the front sight ARE a standard size. There were many aftermarket accessories made that will fit this thread size. Your Walther (and older HW and Diana models) use a 17 mm "M17" thread.
These photos show a variable-width front sight post, made years ago by Gehmann for M17 sights--shown here on an HW 55, but fits my Walthers perfectly. It is beautifully made and a treat to use.
Another good option is a fellow named Neil Price in the UK. He custom-makes clear acrylic inserts for the front sight. I have bought a set of Walther inserts from him. He will provide any number you want and any opening size you desire, his prices are reasonable and his service is quick. A wonderful gent to do business with. I believe his addy is firstname.lastname@example.org
This photo shows a set of Neil's front sight inserts, in this case a set of 10 for old Dianas. Note the beautifully machined edge recess, which helps the inserts fit snugly in the front sleeve. When you look at the beveled aperture edge mounted in the sight, you see a nice crisp "floating" black ring element--wonderful.