SRAM S300s look like a good option.

I think I am going to get some "old" modern ten-speed 105 cranks. 24mm spindle and all that.

since this is a singlespeed drivetrain and not a 1x, is there any reason I should not just use the 39t inner chainring instead of buying a singlespeed specific chainring? it's a standard road double, so I could remove the big ring, install some short chainring bolts, and keep the smaller 39t ring. to the best of my knowledge, the 39t on a double ring looks an awful lot like a SS ring.