A 95mm screw-in NDX400 may be hard to find, but there are alternatives. Community answers suggest using large square neutral density filters in the 2.4, 2.7, or 3.0 optical density range (about 8, 9, or 10 stops) with a holder system such as Lee or Cokin, which can also be reused on other lenses.

However, for photographing the sun specifically, a proper full-aperture solar filter is the safer and better choice. Astronomy-style solar filters are designed for direct solar viewing and imaging, and one key advantage is that they are safe to look through with your eyes when used correctly. A standard photographic ND filter only reduces light; it is not necessarily intended for safe direct solar observation.

So: yes, alternatives exist, but if your goal is shooting the sun, look for a dedicated solar filter sized appropriately for the front of the lens rather than relying on a regular ND filter alone.