I've got one of their boring bars and get quite a few cutters and inserts from them all are far eastern but of a good standard.
Gloster tools would be another one to try.
https://www.glostertooling.co.uk/ I have one of their ER16 chucks on the CNC.
As for flats a lot will depend on your machine. My X3 has no easy way to lock the spindle so I have flats on the ER32 but the SX2.7 and KX3 both have a hole at the end of the spindle for a Tommy bar so just use that in one hand and nut spanner in the other.