Is there any drop -in alternate parts available for K78L05-500R3 other than MP-K78L05-500R3

If you don’t need a module that can also do -5V output, the following Murata Power Solutions part may work for you:
7805SR-C Murata Power Solutions Inc. | Power Supplies - Board Mount | DigiKey
Kindly check the specifications to see if it may work for your application.

Here’s a link to a bunch of 7805 drop-in type DC-DC replacements, some of which are more affordable than others. You should check datasheets for any differences which might be relevant in your particular application. Of note is that the Mornsun part had a pretty wide input range, from 6.5V - 36V.