Is that part number a regular 18mm engine block? If so then there are lots of sources. Who is your favorite vendor?
But if you're asking about E motor hooks, then a 24mm engine block is an AR-2050 ring, which is used in lots and lots of kits and is also available from a number of vendors. These rings, of course, are also used to center 18mm tubes in 24mm for motor mounts in many many rockets.
For example, at ASP:
https://www.asp-rocketry.com/ecomme....cfm?cat_id=110
On this page the 5/20 centering rings are also 18mm engine blocks. The 20/50 centering rings are also 24mm engine blocks.
eRockets has both EB-20s (for 18mm motors) and AR-2050s, and for less than buying them from ASP (in small quantities, anyway). Apogee will also have comparable parts, as does BMS among others. (eRockets also has the split AR-2050s as are used for the aft ring in the motor mounts where a motor hook is also used but of course an X-acto blade can make an AR-2-5- into an AR-2050S pretty easily....)
ASP has E engine hooks for only 99 cents:
https://www.asp-rocketry.com/ecomme...nt=57&navPanel=
The ones at eRockets are 2.49 each:
https://www.erockets.biz/semroc-eng...-1pk-sem-eh-45/
But you can make your own engine hooks from the metal stiffening spines of discarded windshield wipers and bend them to any length you want.
That's a start, anyway.
Getting individual parts means going to Apogee or eRockets or ASP or BMS rather than Estes.