Create your own custom font easily. Simply launch FontForge, the top choice for open source font editing, and design a font with your preferred glyph in each letter slot you require support for. Alternatively, you can craft a cmap 13 font, utilizing a single glyph mapped to the entire code range like Adobe's "Blank" font.
After designing your font, opt for the "web open font" format to generate a WOFF2 file rather than a traditional system font like ttf/otf. Once complete, you can load it using an @font-face rule.
However, keep in mind that this method may not significantly enhance password security—it's ultimately up to you to decide whether it's worth implementing.
Regardless, creating the font itself is remarkably straightforward.