agh @pollux just saw your post, don't know how I missed it. Anyway, there isn't currently a level that has what you're saying, but you can set it up easily yourself-- all you need to do is modify the spawnlists. Just edit the text file:
"game/assets/levels/spawnlist_loyalists.json"
you'll see something like:
"min" :
[
["assets/data/units/loyalists/loy_tank_04.json", 1],
["assets/data/units/loyalists/loy_tank_04.json", 1],
["assets/data/units/loyalists/loy_tank_04.json", 2],
["assets/data/units/loyalists/loy_tank_04.json", 2],
["assets/data/units/loyalists/loy_agrav_01.json", 1],
["assets/data/units/loyalists/loy_agrav_01.json", 1],
["assets/data/units/loyalists/loy_agrav_01.json", 2],
["assets/data/units/loyalists/loy_agrav_01.json", 2],
["assets/data/units/loyalists/loy_tank_03.json", 2],
["assets/data/units/loyalists/loy_tank_03.json", 2],
["assets/data/units/loyalists/loy_tank_03.json", 1],
["assets/data/units/loyalists/loy_tank_03.json", 1],
["assets/data/units/loyalists/loy_tank_02.json", 1],
["assets/data/units/loyalists/loy_foot_01.json", 10],
["assets/data/units/loyalists/loy_foot_01.json", 10],
["assets/data/units/loyalists/loy_foot_01.json", 10],
["assets/data/units/loyalists/loy_foot_02.json", 6],
["assets/data/units/loyalists/loy_foot_02.json", 6]
],
-------------
each entry is a spawn call, so just get rid of all of those except for the 'loy_foot_01' and 'loy_foot_02' calls, and add more to your heart's content. The number after the call is how many units spawn per call. I have no idea what the upper limit of spawnable units is, but you should be able to get a few hundred in at least.
Also, some commands you may find useful (use '~' to open console):
devmode 1 (enables 'q' to teleport as well as other stuff)
god 1 (invulnerability)
invisible 1 (derp)
Played the demo for a good 30 minutes. It's pretty fun. Please tell me you have a test level somewhere where I can chaingun through like 20,000 of those little soldiers? That would be so satisfying.