I have a backup of the 5.24 Commercial Edition Patch thanks to another helpful user. So, if you have the Commercial Edition license, you could use that patch instead 5.51/5.52. I personally think that using 6.60 instead of 5.51/5.52 is the better choice because it is more mature and feature complete for BSP-geometry based games. 5.24 on the other hand supports DX7, 8 bit mode and old syntax and 5.51 doesn't. So 5.24 is the best version for old school 3D games. I don't have a backup of 5.51/5.52.
Or you could ask on the Acknex Discord server
if someone has a backup.