Hello friends,
As I was searching neoprene suits for other proposals, I found the company who made the neoprene undersuit. You might know already, but it's nice to share just in case. The company is Yamamoto. They manufacture the best neoprene on the market for several companies, and they even have a reference to Begins in their website.
The company is based in Japan, and they do sell sheets of neoprene. i didn't buy from them since shipping was too expensive to spain *sigh*, but they are extremely polite in the communication.
However, if you are looking for some already made wetsuits EXACTLY like the one Bale wore under the armor, this might help:
Nineplus | Retro Fullsuit
This is the same exact material he wears under the armor. I strongly recommend to look on the fitting table and once you know your perfect wetsuit size, then pick AT LEAST ONE SIZE BIGGER, if not two. Otherwise it's claustrophobic.
I don't come very often in this forum, so if you want to spread the word it would be better.
Keep up the good work guys!