Again does not rhyme with rain, Spain, or plain. I’m sorry, it just doesn’t.
At least not around here it doesn’t. I suppose there is the possibility that someone could be misled to the point where they think again and gain are supposed to rhyme and then someone had the cute idea of calling it an accent, but…no. I do like accents though..except for some canadian accents (in some parts of canada) where a word like mauve rhymes with drove instead of suave.
A few summers ago, AJ and I were walking through St. James park on London with our couchsurfing hosts who had just moved to London after growing up in Australia. We asked them what kind of things were different about the UK compared to Australia and they mentioned that there were these funny little rodents everywhere that they had never seen before. Funny little rodents? They told us that the rodents were apparently known as “Squills” and after a couple moments of confusion they saw one under a tree and pointed it out to us. “Ohhhh, Squirrels!” “Yeh, Squills…isn’t that wot oi sed?”