A lot of kitters are small businesses and some even have lead times. Not sure if they could handle the volume or even want to provide through MD unless md engaged in kitting and using their leverage to order parts (unobtainium)?
Some "mainstream" kits that might be suitable are:
Garage1217 amps (Ember Polaris Horizon Sunrise etc) - entry level desktop class
PM - Starving student amps - entry level
Diy audio - first watt power amp clones
Sokris DAC - diy r2r dac, smd?
Bottlehead (crack, mainline, upgrades) entry level and summit fi tubes
ECP Torpedo 1,3 high end desktop class tube
AMB MCubed midfi desktop solid state, opamps based - never sold as kits
AMB y1, 1.5, 2 dacs/amps, portable or small desktop class, smd - never sold as kits