The DAC can just be a 1-bit DAC, ie. just a buffered version of your comparator signal. Generally speaking there's no repository of designs, what the semiconductor industry usually call IP - although that's a completely inappropriate name for it here. Although I do have an op-amp design that was part of a bandgap that you are free to use and modify as you wish: https://github.com/yrrapt/caravel_amsat_txrx_ic