I would have thought that your electrical wholesaler should have been able to loan the heavy duty crimping tool. I know that most wholesalers in the UK can loan one - like the one below.
I have one like the above, that can do most of the extra big sizes needed for battery to starter cables. I don't use it often, but it has paid for itself a few times over.
I did have one like this
until someone "forgot" to return it. Though this only goes up to 25mm cable, whereas the other one will crimp cables over 75mm. (Sorry, not used to USA cable sizes.)