One film that may be right for you is the ADOX CMS 20 , now available in 120 size . According to Fotoimpex ( Berlin ) website, it can be used down to ISO 12 but I have heard of some photographers that go even as low as ISO 4 - 6 . It may be worth trying even if it will cost a litle more to send it from Germany. I enclose a link to the website for Fotoimpex. It use to be a non-problem company to order from.
Good luck and a Happy New Year .