This is outrageous. Dental dams are not only important for use for woman-to-woman contact. They are used for heterosexual contact and for some male homosexual contact as well.
Yeah, it sucks that people don't hear about dental dams more often and that access to them is so limited. But the DIY dams that you mention that are made by cutting open a condom, or equally by cutting open a latex glove (also an important and under-discussed safer sex aid), work great and are cheap and accessible. I think the problem has to do (in part at least) with the way sex-education is often hung up on penis-in-vagina sex. If sex educators and the organizations that supply condoms (and everybody else for that matter) could get the conversation rolling about all the different activities that constitute sex for people (such variation!) and be more on the ball about talking about the other uses for condoms (and gloves), then the fact that "real" dams are less available wouldn't matter so much.
I'm glad you're writing about this, though I do think it's important to recognize that dams aren't just for lesbians, but for anybody who has a vagina or gives head to vaginas (be those vaginas on men or women) as well as for anyone who is getting or receiving head on their anus. Dental dams rule!