I think I figured it out after seeing your post, I did some trial and error with regards to punching in some numbers. I do recall a cheat similar to this for ORAS and Sun/Moon back on 3DS. Here's the break down:
1. Get the National Dex number of the Pokemon you want (I will use Bublapedia). So for this example I will use Mew
2. Once you have the National Dex number of the Pokemon you want, in this case the National Dex number for Mew is 151, we will then go to a Decimal to Hexadecimal converter site
3. In the Decimal value number, we will put in Mew's National Dex number, 151. When we hit convert we will get the Hexadecimal number, 97
4. Now for this part, I am just going base off of the pattern with the code. The only part that stays the same is the third chunk of numbers indicated in
bold below. The rest stays the same:
08000000 007709E8
0000xxxx 00000000
5. With the Hexadecimal of 97, we will put in that number where
xxxx is. This part is a bit tricky and I may lose you, lol. You will need to put the number in.. reverse? I'm not sure if that's the correct way of saying it. So for Mew,
0000
9700 <--
Incorrect ,
0000
0097 <--
Correct
Therefore the code to encounter Mew in the Wild will be 08000000 007709E8
00000097 00000000
Let's try another Pokémon, Jirachi [National Code is 251, Hex code is 181]
0000
1810 <--
Incorrect
0000
0181 <--
Correct
Therefore the code to encounter Jirachi in the Wild will be 08000000 007709E8 0000
0181 00000000
Let's try another Pokémon, Zacian [National Dex code is 888, Hex code is 378]
0000
3780 <--
Incorrect
0000
0378 < --
Correct
Therefore the code to encounter Zacian in the Wild will be 08000000 007709E8 0000
0378 00000000
Do you see the pattern here?
-- EDIT: I can't post a hyperlink to Bulbapedia and the Decimal to Hexadecimal converter site
Just Google them and I'm sure you'll find one that'll pop up!
Here you got mate! We can follow the same pattern with the whole dex
[Always Encounter (M) (Hold R)]
04000000 00770A20 B9402A68
04000000 00770A4C B9402A61
04000000 00770A58 79405A61
04000000 00770B1C B9402A60
04000000 00770B24 79405A61
04000000 00770B80 B9402A60
04000000 00770B84 79405A61
80000080
04000000 00770A20 18FFFE68
04000000 00770A4C 18FFFD01
04000000 00770A58 18FFFC81
04000000 00770B1C 18FFF680
04000000 00770B24 18FFF621
04000000 00770B80 18FFF360
04000000 00770B84 18FFF321
20000000
[Mewtwo]
08000000 007709E8 00000096 00000000
[Mew]
08000000 007709E8 00000097 00000000
[Celebi]
08000000 007709E8 000000FB 00000000
[Jirachi]
08000000 007709E8 00000181 00000000
[Cobalion]
08000000 007709E8 0000027E 00000000
[Terrakion]
08000000 007709E8 0000027F 00000000
[Virizion]
08000000 007709E8 00000280 00000000
[Reshiram]
08000000 007709E8 00000283 00000000
[Zekrom]
08000000 007709E8 00000284 00000000
[Kyurem]
08000000 007709E8 00000286 00000000
[Keldeo]
08000000 007709E8 00000287 00000000
[Cosmog]
08000000 007709E8 00000315 00000000
[Cosmoem]
08000000 007709E8 00000316 00000000
[Solgaleo]
08000000 007709E8 00000317 00000000
[Lunala]
08000000 007709E8 00000318 00000000
[Necrozma]
08000000 007709E8 00000320 00000000
[Marshadow]
08000000 007709E8 00000322 00000000
[Zeraora]
08000000 007709E8 00000327 00000000
[Meltan]
08000000 007709E8 00000328 00000000
[Melmetal]
08000000 007709E8 00000329 00000000
[Galar-Ponyta]
08000000 007709E8 0000004D 00000001
[Galar-Corsola]
08000000 007709E8 000000DE 00000001
[Larvitar]
08000000 007709E8 000000F6 00000000
[Lotad]
08000000 007709E8 0000010E 00000000
[Sableye]
08000000 007709E8 0000012E 00000000
[Lunatone]
08000000 007709E8 00000151 00000000
[Croagunk]
08000000 007709E8 000001C5 00000000
[Solosis]
08000000 007709E8 00000241 00000000
[Vullaby]
08000000 007709E8 00000275 00000000
[Spritzee]
08000000 007709E8 000002AA 00000000
[Goomy]
08000000 007709E8 000002C0 00000000
[Oranguru]
08000000 007709E8 000002FD 00000000
[Drampa]
08000000 007709E8 0000030C 00000000
[Eiscue]
08000000 007709E8 0000036B 00000000
[Zamazenta]
08000000 007709E8 00000379 00000000
[Zacian]
08000000 007709E8 00000378 00000000
[Bulbassaur]
08000000 007709E8 00000001 00000000
[Squirtle]
08000000 007709E8 00000007 00000000
[Alola-Meowth]
08000000 007709E8 00000034 00000001
[Ponyta]
08000000 007709E8 0000004D 00000000
[Corsola]
08000000 007709E8 000000DE 00000000
[Rowlet]
08000000 007709E8 000002D2 00000000
[Litten]
08000000 007709E8 000002D5 00000000
[Popplio]
08000000 007709E8 000002D8 00000000
[Charmander]
08000000 007709E8 00000004 00000000
[Galar-Meowth]
08000000 007709E8 00000034 00000002
[Grookey]
08000000 007709E8 0000032A 00000000
[Scorbunny]
08000000 007709E8 0000032D 00000000
[Sobble]
08000000 007709E8 00000330 00000000
[Cubfu]
08000000 007709E8 0000037B 00000000
[Zarude]
08000000 007709E8 0000037D 00000000