Take a look at Somma, Somma Tool - Welcome and Schlitter Tool HexMaster Hexmaster Rotary Broach
Are company uses these two but mainly Somma. My company external broaches splines on shafts 2000 to 3000 a day. Purchased an Somma internal for toolroom and have been doing a 8mm hex in stainless .550 dp. on a Mori sl153. Works good, in my experiance rpm is the key, nothing less than 1800, I have been running around 2000 to 2500. Feed around .004 to .006 ipr.