I've not seen any custom smiths offering barrels for the HTI as of yet, but there is certainly a market for them (or at least there will be once a .50BMG nation-wide ban hits).
Also, I have not seen the specs for the HTI barrels/fluting (which I have for the SRS). If you've got those, getting a smith to make the barrel for you shouldn't be TOO big a deal as long as DTA will sell the barrel extensions like they have done thus far for the SRS.
DTA told me that an armorers kit is needed to align the barrel extensions and that they haven't sold any yet for the HTI. Is anyone doing these barrels without the kit?