I do not have a Tool Room Lathe from Haas, but have looked at them in the past. If memory serves me, they have an A2-6 spindle nose on them. That being the case, get their hydraulic closer option and contact ATS Workholding in Rancho Santa Margarita, California, or Hardinge in Elmira, NY.
They both sell collet setups for "C", "J", and "S" type collets. 3J collets are good to 1.75" round stock. I know that the "S" type goes at least to 2" round stock, maybe larger. For that matter, when you are talking to your Haas sales person, tell them what size stock you want to hold in your collet and they should be able to get the machine setup for you from the factory with the collet, if you buy the machine new.
When we bought our SL-10, we ordered a 16C collet closer for it in addition to the 3 jaw chuck. If you go about it that way, as we did, the chuck manufacturer will make sure you have the correct draw tube to collet adapter you need to make things work.
I hope this information helps a little bit.