It is weird that no company makes them. I use 600w conversion bulbs, no complaints.
600w conversion bulbs produce the same spectrum. Sunmaster makes a pretty good one. 600w for mothers is overkill though. 400w mh is fine for aggressive re-growth. T5/T8s are fine for the average grower.
The 400w MH would be more efficient and the perfect choice for what you are trying to do. I am in the same boat. I need to get 60 clones every 8-10 wks from 4-6 mothers. I am using a sunleaves pioneer 4 T5 currently but only because I already have it. If I was starting from scratch I would invest in a 400w MH system.