Yes, there are. But i wouldn't recommend them with a 1x7 setup. Unfortunately these setups do suffer from dropped chains without a FD or other chain retention guide. But at that point, how much are you really saving from the 3x7 setup? Two rings and a front shifter. Which is why I rarely setup my bikes this way. Single-speed you can lose enough stuff to make it worthwhile, but IMO as long as you have a cassette and RD you might as well have the extra ring or two and a FD.

Single-speed/fixed gear without a RD (so, using horizontal dropouts) is nice because if you set it up right the chain will never drop.