>>1455767a vanishingly small amount of bikes have bolt on drop outs, so you just bolt what ever you want into place
but its unlikely you find one for reasonable price
the Walmart type bso bikes are slowly staring to introduce 1x7 type bikes with just the rear derailleur
that is much like what you describe
>>1455762even in that case there is not much fore and aft adjustment
so it limits the combinations of front and rear cogs that can be used
unless a chain tensioner of some sort is used
