Due to the poor breeding practices of the last 60 years (including a massive infusion of pacing Standarbred blood in the middle to late '60s) the gaits of the TN Walking Horse are Alpha Fox Uniform.
If you look at films from the first Celebration and look at a film today you can see just how far the breed has "drifted" from its roots. Some defend this as "diversity." I condemn it as stupidity (and likely cruelty).
So just 'cause you have a TWH does not mean it will do a running walk. Many will not (remember all that pacing blood?). IIRC in Racking Shows classes can be diveded by breeding (Walking Bred or Saddle Bred).
You can teach a pacer to be more centered but it takes some time and some skill. The only device required is a snaffle bit. The gait will be "artificial" (in that it was taught). It will, however, be beneficial in that the horse will not be traveling ventroflexed all the time.
Be very wary of most film depictions of the "running walk." Very few are, in fact, accurate. The running walk is a four beat, isochronal gait with pick up and set down timing being the same. The flat walk is exactly the same, but with a slower cadence. It also included a head nod. Old timers say, "If it ain't noddin', it ain't walkin'". This is quite true. But a nod does not, therefore, mean a running walk.