Seeking answers online, all that came up were these 4 suggestions from a Green Canary yahoo group discussion. This is a really hard issue to get info about and I am grateful that people have shared what works for them.

“Avanti has a spermicide-free polyurethane condom. It *is* lubricated, which causes me very minor irritation (compared to spermicides, other lubricants, and old-fashioned soap and water, it’s nothing), but I deal.”

The argument for vasectomies:  Kids are impossible due to heavy dose medications and lack of oxygen during attacks causes miscarriages. And I can’t go to the hospital if something was to happen, so I’d end up dead. It’s ok, because I never had my heart set on kids anyway.

Allergic to latex which crosses out condoms, diaphragms and femadoms. Get very sick (4 days = 3 weeks in bed) from hormone therapies. Tried about 6 types of pills and have bad reactions to the progesterone. As all implants are also the same as the pills, they are not an option either. And the injections. Being housebound I cannot go for operations so getting my tubes tied, coils or IUDs are also out. Spermicides make me ill. Rhythm method is not possible either. Not safe enough (see no. 1).

 “Our most successful birth control method was using a combination of me using a
combination of methods to determine ovulation times (cervical mucus changes, 
temps, etc..) along with a natural rubber cervical cap. These caps must be 
special ordered to get ones that are not latex. Additionally, they need to be
fitted properly in order to maximize their effectiveness. It is important to 
find a practitioner (midwives tend to be more familiar with them than most
 docs) who has experience fitting them, and sometimes it takes a couple tries 
to get the best fit. It is recommended that they be used in conjunction with
a spermicidal jelly in order to help seal the cap on the cervix. For obvious 
reasons, a biohazard in my vagina was not an option. However, honey has long
 been used as a spermicide. We mixed organic honey 50-50 with filtered water 
and it sealed perfectly. The only reason that we did not continue with this 
method is that it isn’t 100% effective (although I used it for over three years
and didn’t get pregnant….and I’m fertile myrtle in general). This may be an 
option for some people to consider.”

“You really should get the book Taking Charge of Your Fertility; it is about 
the fertility awareness method of birth control which is a lot different than
 the rhythm method. The rhythm method has failed many women because it is
 based on the belief that women’s cycles are all the same, which isn’t true by
 any means and it only relies on temperature taking, which only tells you 
after ovulation has already taken place, which is too late. Your body tells 
you when you are fertile and the signs are easy to read, it is all in the
book, I would put it all down, but it would take too long. Anyway, the book 
is extremely informative and empowering.” I wouldn’t have said “You really should” since it is disempowering, but the idea is good.

Most of the people who replied the next time this came up on Green Canary said abstinence. Some can use diaphragms and condoms without chemicals added. See Resource page about MCS safe sex toys.