Er, are we casually chatting or are you really not understanding and asking something?
You talked about memory map, that's memory. You want to find the "image" in the ROM, not memory (not entirely true, but to get started yes, find them in the ROM first). Since all the images wouldn't be loaded to memory just the ones on the required chunk and only during the "load image function" then the chunk would be unloaded and a better chunk (like battle gui code) would remain in memory most of the time.
So just load the ROM on an hex editor and treat it like the memory viewer, you can even load changes on the emulator and see what they do :P
Yes, Missingno is a placeholder, but not in a separate routine that does "if pokemon not found then go to this specific placeholder", no, the routines just take an index (species number) and search in the data as if it was an array (start + offset*index), and there happens to be values there and they get loaded, the programmers did write MissingNo. in many of them (in some didn't it seems, ending in glitch names), but they didn't give it much thought as a pokemon it seems because all they created for it is the name, there's no sprite, no moveset that makes sense at least, anything that I know. On later gens they created an sprite at least :P
No idea about what the "something else" is, it's possible it's nothing. They could have had all the pokemon data area cover the 256 possible pokemon and just left the data "empty" on the unused spots, and by empty I mean they didn't touch it anymore after development finished so missingno moveset could be leftovers from development.
OE 81 is not ascii for B, it is B in pokemon terms already, I believe the ROM should have the string.
Yup it does, all the pokemon names are stored on an array, so I assume the base stats have their own array and all the stuff separately instead of an array of "struct PokemonSpecie". It starts somewhere at 1BFFC and I could find BULBASAUR and later two MISSINGNO. right next to each other followed by GROWLITHE, it seems they have 50 to signify end of string but if the string is too long they just cut at "max length" of 10 and omit the 50.
That comment by HyperHacker is interesting, but I dont know how the decompressor works to help you with that. If you can't find anything even among rom hackers maybe just maybe loadingNOW. is still active, I think I last saw his nick here
http://www.filb.de , IIRC he used to obtain the images from pokemon games, but not sure if he tackled RBY.