Not sure I understand the reference to a white line. The classic Redfield Sourdough has an angled blade with a brass insert.

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Here is the genuine article on ebay but don't know if this is the size you need.

https://www.ebay.com/itm/406-S-Redf...t-Savage-Winchester-Marlin-/311929241893

If the square profile is the main point then there are lots of patridge style sights available, the XS front sights are commonly made with a white line running up the middle. However, they are made to match the XS peep sight so generally run very tall. If you want just a square blade Skinner makes a nice thin sight in several sizes, both in width and height and can make them in a black matte or solid brass. They are specifically made to be filed down some - if needed - to get the proper height.

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!