not really.. well I guess you could try intermedia and see how big they get(supposed to get 20" in the wild), they're expensive but an awesome bass to have. next smallest I guess would be mono's but they I would imagine should get a few inches bigger than your 24" width tank in 6 years.
make a deal with someone with a larger tank and grow them out. make a profit and do it again.....just make sure they have a home when they out grow the 210.....