How to play a Bot match in Portal with 127 bots?

Have you tried the built in conquest large/solo-co-op mode? (not in portal).

1. From the main menu select All-Out Warfare
2. Click on Change GameMode in the bottom left above Play,
3. select SOLO & CO-OP in the top right
4. To select ai difficulty or map, hover your mouse over Conquest (or breakthrough) and hit F and adjust ai level and/or map and click Done
5. left click to select Conquest (or breakthrough)
6. hit play.

I use this method for testing new guns n stuff all the time, it works really well.