I'm in north NJ as well, our water is better for the CA cichlids. If you think you could get them something bigger down the road in say 6 or 8 months, you could probably grow out a group of convict relatives, buy them small at 1"ish and have some time in a 29. TUIC has some, and there are also a couple of LFS's on route 46 in clifton, since you are in north NJ, that both have good cichlid selections, you might have luck there. But if you want a fish that can live for years in the 29 gallon, I would look to some other smaller fish.
If you really wanted the south american dwarfs, you could get an RO filter. They make some pretty small cheap ones that will get your water suitable for a SA setup, with some additive for minerals, I have used this in the past to keep planted tanks in our water.