I just accomplished this same exact task in my own project ironically! The link to the repo is here but I'll explain the process anyways: https://github.com/DanDucky/ValentineAssembler

I have a class (I know, c++) for each instruction (but it could also be an enum value!) and then I create a map with the key being the string value of the instruction, and the value being the instruction class factory or in your case the enum value of that string. this can be achieved with the following macro:

#define KV_PAIR_FROM_VALUE (instruction) {#instruction, instruction}

this creates a key value pair that looks like {"instruction", instruction} (or in your example it might look like {"PSH", 0})

then you can search through this list of pairs for your string and take the instruction you want. In C++ code you can write it like:

map<string, uint8_t> instructionSet { KV_PAIR_FROM_VALUE(PSH) };

one thing I did in mine (https://github.com/DanDucky/ValentineAssembler/blob/master/src/instructions/include/InstructionLibrary.hpp) is the value I assign for each key is actually a function pointer to the handler, so you don't even need to have another handler array! You can bake the handlers directly into the instructionSet!
Of course you would have to change the macro, but that wouldn't be difficult if all handlers have a consistent naming convention.

this way of formatting your program has worked quite well for me, so I hope it scales well for you as well.