Use a text editor such as notepad to edit the "_reinforcementDefination.lua" file in the "\assets\world\[map name]\scripts" directory in the game folder. Locate lines similar to the following.

rnf_Vehicle[0]['type'] = 'm26' rnf_Vehicle[0]['count'] = 0

Change the "0" to any value to get that number of the corresponding unit (for example, m26) during game play.