I don’t know of any repo to do that. My thought is to take the thethingsnetwork-send-v1 example program from https://github.com/wklenk/lmic-rpi-lora-gps-hat and adapt it to take in command line arguments that specify the various keys needed and allow arbitrary hex data to be specified. example:
ttn-send -a appeui -d deveui -n devkey -s artkey -e devaddr -x hexdata
It should be relatively simple to do. I don’t know how stable lmic is though at this point.