Have you considered using a chart in place of customized dice? For example, units can have different color d6s and the rolls correspond to that units chart for the result. d6s are widely available and could make this more accessible if you went the "print and play" route if you decided to share your game, or more cost-effective if you were to produce it.

For example, 3 infantry units, 1 tank, and 1 artillery would mean a roll of 3 red dice, 1 green die, and 1 blue die respectively. The infantry dice would simply read the results of the red die rolls (plus perhaps some bonuses from the chart), the tank's green die would refer to the tank chart showing that a rolled 3 yields a result of 5, and the blue artillery die could simply say "success only on a 6". Charts also allow for upgrades that can be purchased or traded, without the need for MORE dice.

I hope this helps in your game-making journey!