As in their numbers?
My method is to multiply their pokedex number by 10, and then +100 for each generation. (eg. Celebi is 251, so 2510, +200 for gen 2, = 2710)
Then check every odd number (every 8th file is a model, all models are odd numbers, so open 2711, 2713, 2715 and 2717 and one of them will be a model).
When a model opens, it should be a pokemon near the one you want in the dex. So use the arrow keys on your keyboard to scroll through models to the model you wanted. (In this case, 2715 will open Raikou's model, pressing right 9 times will open Celebi (2787))
Then for the texture files, +2 to the model number for the standard texture, +3 for the shiny textures.
This is only rough, as the first 4 gens have more mega forms and loads of gender differences so they take up more files (also unown, arceus, vivillon and furfrou have a load of forms). And using this, Volcanion (721) gives 7810, when there are actually about 8060 files, and Volcanion is ~8040. But it gets you near enough quickly.
The only pokemon whick don't work in the 'every 8 files' rule, is pumpkaboo and gourgeist, who have more than 16 files per 2 forms.
