Does the FedSuns even do Arti-Regiments ?
I thought it was Battalions assigned to Line RCTs and Companies assigned to Militia RCTs.
Of course I take that to mean SPA myself, tanks, etc.
With 5 Regiments of Infantry I would think at least a platoon/company of Fieldguns for a Regiment is not out of the question at all.
Another option, not mentioned, is the FS Omni Vees can pack in Artillery, though only the Schiltron-Prime as a canon config.
There is also the non-canon Sniper-SPA from BT Magazine.
I'd say your most common are Thumper-ICE of the canon designs.
Just some addition thoughts.
I'd like to see the fluff for the MWDA Sniper & Longtom units when it comes out, the Thumper-ICE was a very nice unit to stick back into canon history, I sincerely HOPE the same happens for the other 2 pieces.