Came by into Days Gone modding nexus looking for this mod but there wasnt any  :( .
Had to learn in Days Gone modding ( Thanks Helios for helping out , and somewhat discord mod community :) )

So after alot of digging up info about hordes - and game files-testing managed to do it. 
Came to conclusion not just boosting numbers but keep a Devs idea about it so here it is - 
Tier 0 200 ( Little Bear Lake Horde - Because obvious its smallest original and sleep in very small house :) , gonna look redicilous as it is (sleep outside hous or on top of heads others)
Tier 1 ( Cascade Region ) 280 (boss horde - 320) Grotto Caves Horde
Tier 2 360 (Belknap Region) (boss horde - 400) Patjens Lakes Horde
Lost Lake Tier 3 (Lost Lake Region) 440 (boss horde - 480) Metolius Lava Cave Horde
Tier 4 (Highway 97 Region ) 520 (boss horde - 580)  Lobert Draw Ridge Horde
Tier 5 (Crater Lake Region ) 600 (boss horde - 670) Mt. Bailey Horde
Ill post a screen of what horde numbers was before :) .

Added 330, 500, 750 and 999 hordes everywhere versions. Maybe yur a hardcore player or dont wanna follow path devs intented . Or its a NGplus for ya.
Anyways to prevent 999 diff versions of this mod spreading here some more options.

***_ It takes time to learn modding for a game- an idea of mod,digging into game files - reading & changing alot in database (especially with current tools state). Wanted to clarify if you feel like doing simpleton almost everything mod replica (even name -_- ) with slightly different numbers, at least ask an author.
It feels opposite to endorsing. I might have my "optional files" for mod half-ready or almost ready. And releasing an 1 option mod just becasue i felt like the sooner the better to share this mod with community and make ppl happy with it :) . _***

Why so little gratitude shown wtih "cough" endorsements , u dont like it? :) 

___________________________
__Got a feedback about that a bug might happen after death loading u might get vanilla horde size so exit to main menu and load up from there.

For me, to make it work I had to START A NEW GAME .  Also might work without a new game if yur early into game and most hordes not spawned yet.
Resetting jobs (hordes) from game pause menu after 100% completion also works.

Ive got a feedback that -  It does work so far as the player has not explored new areas and discovered the horde prior to the mod.
No need to start a new game if you're in early stages or maybe even midway.

Might work Debug option world- player reset spawns, (or smthing like that, my guess it repeats reset hordes and everything after 100% completion) need testing, tell me if worked for ya.  
It was only assumption and debug seems not working. Didnt find anything in there that helped and didnt get any reports about it.
___________________________
Spent many hours making -testing it and putting it up to work , hope yull like it :).

 "pak" version of the mod might not work for some ppl for "mysterious" reasons and i cant do much about it . Rush to a "Death Train" horde to make sure and see if it worked out .Make a save in Copeland camp first time when you get bike. It might be an point of return to install non pak and everything worked.
______________________
Changelog
Version 1.1
For main horde file ( Just fixing some missed values) For 750 version ( Was misplaced with 500 having those entries) . Minor AI tweaks

Version 1.2
File discovered seems to be related with spawns and horde regens that was missed. Spawn waves increased to match new numbers. Shud fix the problem with hordes spawn partially per each encounter also with some horde max numbers doesnt reach intented values. Increased eat-drink time hoping hordes wont spread this much .Minor AI tweaks . Absent folders included into file structure so theres no need to create. Removed unnecessary files.
______________________
INSTALLATION:

Install only 1 version of a mod at once. Optional doesnt require main mod

1st method - unpack rar file into - " :\Users\"Username"\AppData\Local\BendGame\Saved\Cooked\WindowsNoEditor

Create folders that are absent - Included with 1.2 update

After installing mod folder structure should be like this - - Username"\AppData\Local\BendGame\Saved\Cooked\WindowsNoEditor\BendGame\Content\

You will need to go into your game install location and rename the sfpaks folder to something else.
___
2nd method -  "pak" files -  Extract rar so pak ended up into - :\Users\"Username"\AppData\Local\BendGame\Saved\Paks

[Create Paks folder if you do not have it] - Included with 1.2 update

You will need to go into your game install location and rename the sfpaks folder to something else.

Days gone pak mod manager Days gone "pak" mod manager makes it easier installing paks